devscout-rs 0.5.0

// Artifact build/load, fragments cache, incremental reuse.
// Writes are atomic (tmp+rename); fragments cache keying is load-bearing --
// a mismatch makes reuse break silently.
//
// This module owns every serde struct for graph.json + the fragments-cache
// pair (fragments-v18.json, fragments-index-v18.json), plus their path resolution,
// atomic I/O, and the cache-then-resolve-then-write orchestration
// (`rebuild_graph`). The pure resolution ladder that
// turns fragments into `defs`/`edges` lives in `resolve.rs` and returns the
// `Graph` value this module serializes -- see that module for the ladder
// itself.
//
// Schema notes (the on-disk format graph.json must keep):
//   - graph.json is compact JSON with NO indentation:
//     `{"key":value,...}`, no spaces. `serde_json::to_vec` (non-pretty)
//     matches this by default.
//   - Key order is insertion order, not sorted. Defs keep first-insertion
//     order (partial-class duplicates land in
//     `also_in`, not a second top-level entry) -- backed here by a
//     Vec<Def> + HashMap<id, index> pair (`build_def_index` in resolve.rs)
//     rather than a HashMap alone, which has no defined iteration order.
//   - `also_in` is omitted entirely (not `[]`) when a def has no additional
//     declaring sites -- `#[serde(skip_serializing_if = "Vec::is_empty")]`.
//   - `edges` are shape-heterogeneous by `kind`: inherits/uses-type/
//     uses-member share `{kind, from_file, from_line, to, to_file}`;
//     imports is `{kind, from_file, from_line, target}`; ambiguous is
//     `{kind, origin, from_file, from_line, raw, candidates,
//     candidate_count}`. Modeled as an internally-tagged enum
//     (`#[serde(tag = "kind")]`) -- serde always emits the tag field first,
//     matching every one of these shapes' field order.
//   - a `uses-member` edge appends three more keys AFTER that shared prefix,
//     in this exact order: `heuristic` (omitted when precise), `tier`, then
//     `member`. `tier` names WHICH guess tier emitted the row and is present
//     exactly when `heuristic` is; `member` names the member the reference
//     reads or calls and is written on EVERY uses-member edge, the precise
//     ones included -- it is the one fact the row never carried. Both are
//     omit-when-`None`, so the append-last rule every other added key follows
//     holds here too; the other two flagged kinds (inherits, uses-type) stay
//     exactly as they were.
//   - `schema_version` is `GRAPH_SCHEMA_VERSION`, which the `tier`/`member`
//     append above moved to 2. `rebuild_graph`'s unchanged fast path reads
//     the first bytes of an existing graph.json and refuses to reuse one
//     written at an older version, so a stale artifact is rebuilt on the next
//     `map` even when not one fragment moved.
//   - `units` is the LAST key of the whole object, appended after `names`
//     and omitted entirely (not `[]`) when the repo declares no `.csproj` --
//     so a tree without one serializes byte-for-byte as it did before the
//     project model existed. Each row's own key order is fixed too: `id`,
//     `name`, then `refs` (omitted when the project references nothing) and
//     `test` (omitted when false). A unit's DIRECTORY is not persisted: it
//     is `id`'s parent, recomputed on read (`project::units_from_graph`),
//     and neither is per-file/per-def membership -- that is derived from the
//     unit list by `ProjectModel` rather than stored.
//   - `stats.edges_by_kind` has a FIXED key order (inherits, uses-type,
//     imports, uses-member, ctor-di) -- not
//     alphabetical, not insertion order of first edge seen. A plain struct
//     with that declared field order reproduces it.
//   - `stats.ambiguous_pct` is `round(x*1000)/10`: a number that prints
//     WITHOUT a decimal point when whole (`20`, not `20.0`) and with
//     exactly one decimal digit otherwise (`33.3`). Rust's f64 Serialize
//     (ryu-backed) does not reproduce this -- see `Percent1` below, which
//     stores tenths as an integer and branches serialize_i64/serialize_f64
//     so whole values come out as bare integers, without needing serde_json's
//     `arbitrary_precision`/`raw_value` features (neither is enabled).
//   - fragments.json / fragments-index.json are objects keyed by
//     repo-relative path, in file-walk order (fragments-index.json is
//     rebuilt by iterating the same cache object fragments.json used).
//     A `HashMap` has no serialization order guarantee and `serde_json`'s
//     default `Map` (no `preserve_order` feature, which is off here) sorts
//     by key -- neither matches. `OrderedMap<V>` below hand-rolls
//     Serialize/Deserialize (using serde's own `SerializeMap` / `MapAccess`
//     traits, not a bespoke JSON writer) to preserve insertion order.
//   - `built_at_head` records `git -C <root> rev-parse HEAD` (`null` on any
//     failure incl. no commits yet). `manifest.rs` already owns that
//     (`manifest::git_head`) -- `resolve_graph` (resolve.rs) calls THAT, so
//     this module does not duplicate it.

use std::collections::HashMap;
use std::fmt;
use std::fs;
use std::io;
use std::io::Read;
use std::marker::PhantomData;
use std::path::{Path, PathBuf};
use std::sync::atomic::{AtomicU64, Ordering};

use serde::de::{MapAccess, Visitor};
use serde::ser::SerializeMap;
use serde::{Deserialize, Deserializer, Serialize, Serializer};

use crate::extract;
use crate::repo::{git_common_dir, scout_dir};

// ---------------------------------------------------------------------------
// Path resolution (private helpers for the graph directory and cache paths).
// ---------------------------------------------------------------------------

// The def/ref graph lives in the git COMMON dir (shared by every linked
// worktree, alongside the manifest), one level down; a non-git root falls
// back to `<root>/.scout/graph/`.
fn graph_dir(root: &Path) -> PathBuf {
    match git_common_dir(root) {
        Some(common) => common.join("scout").join("graph"),
        None => scout_dir(root).join("graph"),
    }
}

/// Path to the graph artifact (`graph.json`) for `root`.
pub fn graph_json_path(root: &Path) -> PathBuf {
    graph_dir(root).join("graph.json")
}

/// Path to the project-model staleness sidecar for `root`.
///
/// Holds exactly the bytes `graph.json`'s `units` array would carry -- the
/// serialized `Vec<GraphUnit>` and nothing else. `map` compares this file
/// against a freshly discovered model to notice a `.csproj` edit, which no
/// mtime in the fragments index can see: `.csproj` is not a `SOURCE_EXT`, so
/// editing one moves no graph file and `index_is_stale` stays false. Written
/// by `rebuild_graph` only when a model exists and DELETED when one does not,
/// so a repo that never had a `.csproj` never grows the file and one whose
/// last `.csproj` was removed still sees a difference on the next run.
pub fn project_units_path(root: &Path) -> PathBuf {
    graph_dir(root).join("project-units.json")
}

// The version in both cache filenames is the fragment SCHEMA version, bumped
// whenever the extractor starts recording something old cached fragments
// lack -- v10 added def `type_params`/`base_generic_args` and the new
// `ctor-param` ref kind (with its `args` field), v11 added markup graph
// facts (a `.xaml` file's fragment now carries the `x:Class` def and its
// element/`x:Bind` refs, where every cached markup fragment before it carried
// names only), v12 added the TS/JS reference fragment, v13 added def
// `propertyTypes` and ref `receiverPropertyOwner` plus the ref
// `receiverCallOwner`/`receiverCallMember` pair, plus the foreach
// element-type fact -- no new field (it settles into the existing
// `receiver_type`), but a cached fragment from before it can still disagree
// with a fresh one for the same unchanged file, so it rides the same bump
// rather than skipping it. v16 added the ref `receiverBase` flag, set only
// for a `base.` qualifier -- a cached v15 fragment carries none, so every
// `base.` receiver would silently resolve (or fail to resolve) as if it
// were a plain `this.` receiver. v17 added no field: the extractor now
// blanks the inactive arms of `#if`/`#else` groups before parsing, so a
// cached v16 fragment of an unchanged file can carry twin defs and refs
// from both arms that a fresh one no longer records -- the same
// "disagrees for an unchanged file" case that moved v13, so it rides a
// bump too. v18 added def `methodParams` and ref `receiverLambda`, the
// untyped-lambda-parameter callee slot -- a cached v17 fragment carries
// neither, so every per-overload parameter shape and every untyped-lambda
// callee-slot lookup they back would silently see no candidates. The
// rename IS the invalidation mechanism:
// pre-bump caches stop being found, every file reparses
// once, no reader carries version-compat logic. Writers delete every
// superseded generation (see `remove_superseded_caches`).
fn fragments_cache_path(root: &Path) -> PathBuf {
    graph_dir(root).join("fragments-v18.json")
}

fn fragments_index_path(root: &Path) -> PathBuf {
    graph_dir(root).join("fragments-index-v18.json")
}

// Every generation below the current one, not just the immediately previous:
// a repo mapped last under v1 and never since would otherwise keep its v1
// pair forever.
const SUPERSEDED_CACHE_FILES: &[&str] = &[
    "fragments.json",
    "fragments-index.json",
    "fragments-v2.json",
    "fragments-index-v2.json",
    "fragments-v3.json",
    "fragments-index-v3.json",
    "fragments-v4.json",
    "fragments-index-v4.json",
    "fragments-v5.json",
    "fragments-index-v5.json",
    "fragments-v6.json",
    "fragments-index-v6.json",
    "fragments-v7.json",
    "fragments-index-v7.json",
    "fragments-v8.json",
    "fragments-index-v8.json",
    "fragments-v9.json",
    "fragments-index-v9.json",
    "fragments-v10.json",
    "fragments-index-v10.json",
    "fragments-v11.json",
    "fragments-index-v11.json",
    "fragments-v12.json",
    "fragments-index-v12.json",
    "fragments-v13.json",
    "fragments-index-v13.json",
    "fragments-v14.json",
    "fragments-index-v14.json",
    "fragments-v15.json",
    "fragments-index-v15.json",
    "fragments-v16.json",
    "fragments-index-v16.json",
    "fragments-v17.json",
    "fragments-index-v17.json",
];

fn remove_superseded_caches(root: &Path) {
    for name in SUPERSEDED_CACHE_FILES {
        // Best-effort cleanup only -- a leftover superseded file is inert.
        let _ = fs::remove_file(graph_dir(root).join(name));
    }
}

// ---------------------------------------------------------------------------
// Atomic writes -- tmp file in the SAME directory as the target (so
// the final `rename` is same-filesystem and therefore atomic), unique name
// so concurrent writers (this process's own sequential graph/fragments/index
// writes, or a genuinely concurrent process) never collide. Writing to a
// tmp file and renaming is a deliberate upgrade over an in-place write --
// output BYTES are unaffected, only the write's crash-safety.
// ---------------------------------------------------------------------------

static TMP_COUNTER: AtomicU64 = AtomicU64::new(0);

fn atomic_write_bytes(path: &Path, bytes: &[u8]) -> io::Result<()> {
    let dir = path.parent().unwrap_or_else(|| Path::new("."));
    fs::create_dir_all(dir)?;
    let file_name = path
        .file_name()
        .and_then(|n| n.to_str())
        .unwrap_or("artifact");
    let counter = TMP_COUNTER.fetch_add(1, Ordering::Relaxed);
    let tmp_path = dir.join(format!(".{file_name}.tmp.{}.{counter}", std::process::id()));
    let write_result = fs::write(&tmp_path, bytes);
    if write_result.is_err() {
        let _ = fs::remove_file(&tmp_path);
        write_result?;
    }
    fs::rename(&tmp_path, path)?;
    Ok(())
}

fn atomic_write_json<T: Serialize>(path: &Path, value: &T) -> io::Result<()> {
    let bytes = serde_json::to_vec(value).map_err(io::Error::other)?;
    atomic_write_bytes(path, &bytes)
}

// ---------------------------------------------------------------------------
// Insertion-ordered string-keyed map -- backs fragments.json's `{rel:
// {mtime, fragment}}` and fragments-index.json's `{rel: mtime}`. A HashMap
// has no defined iteration order and serde_json's default Map serializer
// (the `preserve_order` feature is not enabled) sorts by key; neither
// matches the required file-walk-order construction. Built on serde's own
// SerializeMap/MapAccess traits,
// not a hand-rolled JSON writer -- serde_json still owns the actual byte
// encoding.
// ---------------------------------------------------------------------------

#[derive(Debug, Clone, PartialEq)]
/// Represents `OrderedMap`.
pub struct OrderedMap<V> {
    entries: Vec<(String, V)>,
    index: HashMap<String, usize>,
}

impl<V> OrderedMap<V> {
    /// Creates an empty insertion-ordered map.
    pub fn new() -> Self {
        Self {
            entries: Vec::new(),
            index: HashMap::new(),
        }
    }

    /// Insert, or overwrite in place when the key already exists --
    /// preserves that key's ORIGINAL position, like assigning to an existing
    /// key on a JSON object.
    pub fn insert(&mut self, key: String, value: V) {
        match self.index.get(&key) {
            Some(&i) => self.entries[i].1 = value,
            None => {
                self.index.insert(key.clone(), self.entries.len());
                self.entries.push((key, value));
            }
        }
    }

    /// Returns the value associated with `key`, if present.
    pub fn get(&self, key: &str) -> Option<&V> {
        self.index.get(key).map(|&i| &self.entries[i].1)
    }

    /// Returns the number of entries.
    pub fn len(&self) -> usize {
        self.entries.len()
    }

    /// Returns whether the map contains no entries.
    pub fn is_empty(&self) -> bool {
        self.entries.is_empty()
    }

    /// Iterates over entries in insertion order.
    pub fn iter(&self) -> impl Iterator<Item = (&String, &V)> {
        self.entries.iter().map(|(k, v)| (k, v))
    }
}

impl<V> Default for OrderedMap<V> {
    fn default() -> Self {
        Self::new()
    }
}

impl<V: Serialize> Serialize for OrderedMap<V> {
    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
        let mut map = serializer.serialize_map(Some(self.entries.len()))?;
        for (k, v) in &self.entries {
            map.serialize_entry(k, v)?;
        }
        map.end()
    }
}

impl<'de, V: Deserialize<'de>> Deserialize<'de> for OrderedMap<V> {
    fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
        struct OrderedMapVisitor<V>(PhantomData<V>);

        impl<'de, V: Deserialize<'de>> Visitor<'de> for OrderedMapVisitor<V> {
            type Value = OrderedMap<V>;

            fn expecting(&self, f: &mut fmt::Formatter) -> fmt::Result {
                f.write_str("a JSON object")
            }

            fn visit_map<A: MapAccess<'de>>(self, mut map: A) -> Result<Self::Value, A::Error> {
                let mut out = OrderedMap::new();
                while let Some((k, v)) = map.next_entry::<String, V>()? {
                    out.insert(k, v);
                }
                Ok(out)
            }
        }

        deserializer.deserialize_map(OrderedMapVisitor(PhantomData))
    }
}

// ---------------------------------------------------------------------------
// `stats.ambiguous_pct` -- see module header. Stored as tenths (an i64) so
// the "is this whole?" branch is exact integer arithmetic, never a float
// epsilon comparison.
// ---------------------------------------------------------------------------

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
/// Represents `Percent1`.
pub struct Percent1(pub i64);

impl Percent1 {
    /// Returns a zero percentage value.
    pub fn zero() -> Self {
        Percent1(0)
    }

    /// `ambiguous_pct` as `round((ambiguous / attempts) * 1000) / 10`, or 0
    /// when there are no attempts. Takes the pre-division inputs so the
    /// rounding happens exactly once.
    pub fn from_ratio(numerator: usize, denominator: usize) -> Self {
        if denominator == 0 {
            return Percent1::zero();
        }
        let raw = (numerator as f64 / denominator as f64) * 1000.0;
        Percent1(raw.round() as i64)
    }
}

impl Serialize for Percent1 {
    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
        if self.0 % 10 == 0 {
            serializer.serialize_i64(self.0 / 10)
        } else {
            serializer.serialize_f64(self.0 as f64 / 10.0)
        }
    }
}

impl<'de> Deserialize<'de> for Percent1 {
    fn deserialize<D: Deserializer<'de>>(deserializer: D) -> Result<Self, D::Error> {
        let v = f64::deserialize(deserializer)?;
        Ok(Percent1((v * 10.0).round() as i64))
    }
}

// ---------------------------------------------------------------------------
// graph.json schema.
// ---------------------------------------------------------------------------

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
/// Represents `AlsoIn`.
pub struct AlsoIn {
    /// The file value.
    pub file: String,
    /// The line value.
    pub line: usize,
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
/// Represents `Def`.
pub struct Def {
    /// The id value.
    pub id: String,
    /// The name value.
    pub name: String,
    /// The namespace value.
    pub namespace: String,
    /// The kind value.
    pub kind: String,
    /// The file value.
    pub file: String,
    /// The line value.
    pub line: usize,
    /// The methods value.
    pub methods: Vec<String>,
    /// Test-coverage stage -- the one member fact that SURVIVES onto disk
    /// (`properties`/`fields`/`extensionMethods`/`bases` are resolution inputs
    /// only, stripped before the row is written): `devscout tests` reads it back
    /// out of graph.json. Positioned after `methods` and before `also_in`, and
    /// omitted when empty, so a def declaring no tests keeps its exact
    /// pre-stage bytes.
    #[serde(default, rename = "testMethods", skip_serializing_if = "Vec::is_empty")]
    pub test_methods: Vec<String>,
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    /// The also in value.
    pub also_in: Vec<AlsoIn>,
    #[serde(default, rename = "endLine", skip_serializing_if = "is_zero")]
    /// The end line value.
    pub end_line: usize,
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
/// Represents `Candidate`.
pub struct Candidate {
    /// The id value.
    pub id: String,
    /// The file value.
    pub file: String,
}

/// Which heuristic tier emitted a guess.
///
/// The two differ by an order of magnitude in precision and `heuristic: true`
/// alone cannot tell them apart: `Ext` is C#'s own extension-method lookup run over a recorded
/// `(member, this-type)` bucket -- a real rule, only unverifiable against an
/// out-of-graph receiver -- while `Guess` is the scored tier picking by NAME
/// among the defs that happen to declare a member so called.
#[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum HeuristicTier {
    /// Tier (f): extension-method lookup.
    Ext,
    /// The scored tier: a name guess.
    Guess,
}

/// The guess tag, appended LAST on every edge kind that can
/// carry it. `heuristic: true` is set only on an edge a heuristic tier
/// emitted and never writes `heuristic: false`, so this side pairs
/// `skip_serializing_if` with `default`: absent == precise, and a precise
/// edge's bytes are exactly what they were before the tag existed. Only
/// the resolver's heuristic tiers set it today (both
/// `uses-member`), but the flag lives on all three targeted kinds because
/// the query layer's heuristic adjacency is kind-keyed, so a future tier
/// tagging a `uses-type` edge needs no schema change.
///
/// `uses-member` carries two more appended keys, `tier` then `member`, in
/// that order and NOT mirrored onto the other two kinds: neither has a
/// member to name, and no tier tags one today. `tier` splits the umbrella
/// flag into the two tiers a reader can act on differently; `member` names
/// the member the reference reads or calls and is written on every
/// uses-member edge, precise ones included, because "which member" is a fact
/// about the reference rather than about the guess. Both are
/// omit-when-`None`, so a reader of the old shape sees only added keys.
///
/// The next slot on this variant is reserved for `source: Option<Provenance>`
/// (`"semantic"` for an edge a real compiler vouched for), appended after
/// `member` and omitted when empty, on the same rule.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
#[serde(tag = "kind")]
pub enum Edge {
    #[serde(rename = "inherits")]
    /// Represents `Inherits`.
    Inherits {
        /// The value value.
        from_file: String,
        /// The value value.
        from_line: usize,
        /// The value value.
        to: String,
        /// The value value.
        to_file: String,
        #[serde(default, skip_serializing_if = "is_false")]
        /// The value value.
        heuristic: bool,
    },
    #[serde(rename = "uses-type")]
    /// Represents `UsesType`.
    UsesType {
        /// The value value.
        from_file: String,
        /// The value value.
        from_line: usize,
        /// The value value.
        to: String,
        /// The value value.
        to_file: String,
        #[serde(default, skip_serializing_if = "is_false")]
        /// The value value.
        heuristic: bool,
    },
    #[serde(rename = "uses-member")]
    /// Represents `UsesMember`.
    UsesMember {
        /// The value value.
        from_file: String,
        /// The value value.
        from_line: usize,
        /// The value value.
        to: String,
        /// The value value.
        to_file: String,
        #[serde(default, skip_serializing_if = "is_false")]
        /// The value value.
        heuristic: bool,
        #[serde(default, skip_serializing_if = "Option::is_none")]
        /// Which guess tier emitted this edge -- `Some` exactly when
        /// `heuristic` is true. Build the variant through
        /// `Edge::uses_member`, which derives one from the other.
        tier: Option<HeuristicTier>,
        #[serde(default, skip_serializing_if = "Option::is_none")]
        /// The member this reference reads or calls, on precise and
        /// heuristic edges alike. `None` only for a reference the extractor
        /// recorded no member name for.
        member: Option<String>,
    },
    #[serde(rename = "imports")]
    /// The value value.
    Imports {
        /// The source file.
        from_file: String,
        /// The source line.
        from_line: usize,
        /// The imported target.
        target: String,
    },
    #[serde(rename = "ambiguous")]
    /// Represents `Ambiguous`.
    Ambiguous {
        /// The value value.
        origin: String,
        /// The value value.
        from_file: String,
        /// The value value.
        from_line: usize,
        /// The value value.
        raw: String,
        /// The value value.
        candidates: Vec<Candidate>,
        /// The value value.
        candidate_count: usize,
    },
    /// Constructor-parameter DI resolution (see resolve.rs's
    /// `resolve_ctor_param`). Field order (`kind`, `from_file`, `from_line`,
    /// `iface`, `resolution`, `args`, `to`, `candidates`) is significant --
    /// it fixes the serialized field order.
    /// `iface` is the injected type's bare identifier; `args` its closed
    /// generic arguments, present only when it has any; `to` the resolved
    /// implementation's def id, present only for 'plain'/'closed'/
    /// 'open-generic'; `candidates` the capped, sorted tie list, present only
    /// for 'ambiguous'.
    #[serde(rename = "ctor-di")]
    CtorDi {
        /// The value value.
        from_file: String,
        /// The value value.
        from_line: usize,
        /// The value value.
        iface: String,
        /// The value value.
        resolution: String,
        #[serde(default, skip_serializing_if = "Option::is_none")]
        /// The value value.
        args: Option<Vec<String>>,
        #[serde(default, skip_serializing_if = "Option::is_none")]
        /// The value value.
        to: Option<String>,
        #[serde(default, skip_serializing_if = "Vec::is_empty")]
        /// The value value.
        candidates: Vec<Candidate>,
    },
    /// A TS/TSX module import. Distinct from `imports` (C#'s
    /// `using` directive, which names a NAMESPACE and resolves to no file):
    /// `target` is the specifier as written and `to_file` the file it
    /// resolved to. `via` is appended LAST and present only on a
    /// barrel-followed edge, naming the module the source literally imported
    /// so a reader can tell the routing table apart from the dependency.
    #[serde(rename = "import")]
    Import {
        /// The value value.
        from_file: String,
        /// The value value.
        from_line: usize,
        /// The value value.
        target: String,
        /// The value value.
        to_file: String,
        #[serde(default, skip_serializing_if = "Option::is_none")]
        /// The value value.
        via: Option<String>,
    },
    /// A call or `new` naming an imported or locally-exported
    /// declaration.
    #[serde(rename = "call")]
    /// The value value.
    Call {
        /// The source file.
        from_file: String,
        /// The source line.
        from_line: usize,
        /// The target definition identifier.
        to: String,
        /// The target file.
        to_file: String,
    },
    /// A JSX tag naming a component declaration.
    #[serde(rename = "jsx-use")]
    /// The value value.
    JsxUse {
        /// The source file.
        from_file: String,
        /// The source line.
        from_line: usize,
        /// The target definition identifier.
        to: String,
        /// The target file.
        to_file: String,
    },
    /// An action creator or thunk handed to a dispatching call
    /// (`dispatch(...)`, `ofType(...)`).
    #[serde(rename = "dispatch")]
    /// The value value.
    Dispatch {
        /// The source file.
        from_file: String,
        /// The source line.
        from_line: usize,
        /// The target definition identifier.
        to: String,
        /// The target file.
        to_file: String,
    },
}

impl Edge {
    /// The guess tier that emitted this edge, or `None` on a precise one --
    /// and on every kind that carries no tier at all, which is every kind but
    /// `uses-member`.
    pub fn tier(&self) -> Option<HeuristicTier> {
        match self {
            Edge::UsesMember { tier, .. } => *tier,
            _ => None,
        }
    }

    /// Whether the edge declares itself a guess, across the three kinds that
    /// can carry the flag.
    pub fn is_heuristic(&self) -> bool {
        match self {
            Edge::Inherits { heuristic, .. }
            | Edge::UsesType { heuristic, .. }
            | Edge::UsesMember { heuristic, .. } => *heuristic,
            _ => false,
        }
    }

    /// The one way to build a `uses-member` edge. `heuristic` is DERIVED from
    /// `tier` rather than passed alongside it, so the two cannot disagree: a
    /// tagged edge is always flagged, a flagged edge always names its tier,
    /// and no emit site can grow a third state by forgetting a field.
    pub fn uses_member(
        from_file: String,
        from_line: usize,
        to: String,
        to_file: String,
        member: Option<String>,
        tier: Option<HeuristicTier>,
    ) -> Edge {
        Edge::UsesMember {
            from_file,
            from_line,
            to,
            to_file,
            heuristic: tier.is_some(),
            tier,
            member,
        }
    }
}

#[derive(Debug, Clone, Default, PartialEq, Serialize, Deserialize)]
/// Represents `EdgesByKind`.
pub struct EdgesByKind {
    /// The inherits value.
    pub inherits: usize,
    #[serde(rename = "uses-type")]
    /// The uses type value.
    pub uses_type: usize,
    /// The imports value.
    pub imports: usize,
    #[serde(rename = "uses-member")]
    /// The uses member value.
    pub uses_member: usize,
    /// Appended LAST, matching the `ctor-di` slot in the fixed key order.
    #[serde(rename = "ctor-di")]
    pub ctor_di: usize,
    /// The four TS edge counts, appended after `ctor-di` in this exact order
    /// and ONLY when the repo carries a TS fragment at all. A C#-only repo's
    /// stats block omits them entirely -- which is why these are `Option` and
    /// not a plain `0`.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub import: Option<usize>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    /// The call value.
    pub call: Option<usize>,
    #[serde(rename = "jsx-use", default, skip_serializing_if = "Option::is_none")]
    /// The jsx use value.
    pub jsx_use: Option<usize>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    /// The dispatch value.
    pub dispatch: Option<usize>,
}

/// `heuristic_edge_count` split by the tier that emitted each edge, in the
/// fixed key order every tier-keyed output uses (ext, then guess).
///
/// Both keys are always written, and `ext + guess` equals `heuristic_edge_count` --
/// including after the heuristic-side dedup, which decrements the dropped
/// edge's own tier.
#[derive(Debug, Clone, Copy, Default, PartialEq, Serialize, Deserialize)]
pub struct HeuristicByTier {
    /// Edges tier (f) emitted.
    pub ext: usize,
    /// Edges the scored tier emitted.
    pub guess: usize,
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
/// Represents `Stats`.
pub struct Stats {
    /// The def count value.
    pub def_count: usize,
    /// The file count value.
    pub file_count: usize,
    /// The edges by kind value.
    pub edges_by_kind: EdgesByKind,
    /// The ambiguous count value.
    pub ambiguous_count: usize,
    /// The ambiguous pct value.
    pub ambiguous_pct: Percent1,
    /// The unresolved external count value.
    pub unresolved_external_count: usize,
    /// Appended LAST, and always serialized (unlike the edge flag above): the
    /// key is written unconditionally, so a graph with no guesses still
    /// carries `"heuristic_edge_count":0`. `default` is for the READ side only
    /// -- a graph.json written before this counter existed has no such key,
    /// and it must read back as 0 rather than fail to parse.
    #[serde(default)]
    pub heuristic_edge_count: usize,
    /// Test-coverage stage -- appended LAST and always serialized, like the
    /// stage-4 counter above it. Counts merged DEF ROWS, not fragment entries,
    /// so a partial test class split across two files is one test def.
    #[serde(default)]
    pub test_def_count: usize,
    /// The TS resolver's own four counters, omitted entirely when the repo
    /// carries no TS fragment (the same omit-when-empty rule every other
    /// appended fact follows). Appended after `test_def_count`, and NOT last
    /// any more: `heuristic_by_tier` below is the newer fact and takes the
    /// tail, so a TS repo's stats block appends in the order the facts were
    /// added rather than interleaving the newest one before an older key.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub ts: Option<crate::tsgraph::TsStats>,
    /// The tier split of `heuristic_edge_count`, appended LAST and always
    /// serialized, like the two counters above it. `default` is for the READ
    /// side only: a graph.json written before the tiers existed has no such
    /// key and must read back as two zeros rather than fail to parse.
    ///
    /// A C#-only repo writes no `ts` key at all, so for such a tree this key
    /// still follows `test_def_count` directly and the bytes are unchanged.
    #[serde(default)]
    pub heuristic_by_tier: HeuristicByTier,
}

/// One row of the full name index. Field order (`name`, `kind`,
/// `file`, `line`, `owner`) is significant; `owner` carries the
/// declaring type's def id for a member and is omitted for a type, an enum
/// member, and every markup or resource key.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct GraphName {
    /// The name value.
    pub name: String,
    /// The kind value.
    pub kind: String,
    /// The file value.
    pub file: String,
    /// The line value.
    pub line: usize,
    #[serde(default, skip_serializing_if = "String::is_empty")]
    /// The owner value.
    pub owner: String,
}

/// One `.csproj` project as graph.json persists it.
///
/// Field order (`id`, `name`, `refs`, `test`) is significant, and the last two are
/// omit-when-empty/omit-when-false: a leaf project that references nothing
/// and is not a test project serializes as just its `id` and `name`.
///
/// Deliberately NOT `project::Unit`: that type also carries `dir`, which is
/// always `id`'s parent directory and so is recomputed on read rather than
/// stored (`project::units_from_graph`). Nothing about which FILE belongs to
/// which unit is persisted either -- `ProjectModel` derives that from the
/// unit list.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub struct GraphUnit {
    /// Repo-relative path to the `.csproj` file, which is also this unit's
    /// identity -- what `refs` entries name.
    pub id: String,
    /// The project name (the csproj file name without its extension).
    pub name: String,
    /// The `id`s of this project's DIRECT `ProjectReference` targets, not
    /// transitively closed. Omitted when empty.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub refs: Vec<String>,
    /// Whether this is a test project. Omitted when false.
    #[serde(default, skip_serializing_if = "is_not_test")]
    pub test: bool,
}

fn is_not_test(b: &bool) -> bool {
    !*b
}

/// The version stamped into every graph.json this build writes, and the one
/// `rebuild_graph` demands before it reuses an artifact it did not just
/// produce.
///
/// Bumped to 2 when `uses-member` edges gained `tier` and `member`:
/// a schema-1 graph is READABLE (both keys default) but it is missing facts
/// the query layer now reports, so it gets rebuilt rather than trusted.
pub const GRAPH_SCHEMA_VERSION: u32 = 2;

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
/// Represents `Graph`.
pub struct Graph {
    /// The schema version value.
    pub schema_version: u32,
    /// The built at head value.
    pub built_at_head: Option<String>,
    /// The defs value.
    pub defs: Vec<Def>,
    /// The edges value.
    pub edges: Vec<Edge>,
    /// The stats value.
    pub stats: Stats,
    /// Appended LAST, after `stats`, and omitted when empty: the
    /// house rule for every added field, and what keeps a graph built over a
    /// set that declares no name byte-identical to what it was.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub names: Vec<GraphName>,
    /// The repo's `.csproj` projects, sorted by `id` -- appended LAST, after
    /// `names`, and omitted entirely when the repo declares none. A tree with
    /// no `.csproj` therefore serializes exactly as it did before the project
    /// model existed.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub units: Vec<GraphUnit>,
}

/// Reads and deserializes the repository graph, returning `None` on failure.
pub fn read_graph(root: &Path) -> Option<Graph> {
    let text = fs::read_to_string(graph_json_path(root)).ok()?;
    serde_json::from_str(&text).ok()
}

fn write_graph(root: &Path, graph: &Graph) -> io::Result<()> {
    atomic_write_json(&graph_json_path(root), graph)
}

// ---------------------------------------------------------------------------
// Fragments cache schema -- the RAW (unresolved) per-file extraction output,
// keyed by repo-relative path. Mirrors extract.rs's DefRecord/UsingRecord/
// RefRecord field-for-field; the serde impls live here rather than on the
// extractor's own types.
// ---------------------------------------------------------------------------

/// Field order is significant: id, name, namespace, kind, line, methods, then
/// the member-fact additions in that exact order -- properties, fields,
/// methodReturns -- and after those extensionMethods, appended LAST. Each is
/// omitted entirely when empty, so a type declaring none of them serializes
/// exactly as it did before those additions.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct FragDef {
    /// The id value.
    pub id: String,
    /// The name value.
    pub name: String,
    /// The namespace value.
    pub namespace: String,
    /// The kind value.
    pub kind: String,
    /// The line value.
    pub line: usize,
    /// The methods value.
    pub methods: Vec<String>,
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    /// The properties value.
    pub properties: Vec<String>,
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    /// The fields value.
    pub fields: Vec<String>,
    /// Member name -> declared return type NAME, in FIRST-DECLARATION SOURCE
    /// ORDER -- deliberately `OrderedMap`, never a `BTreeMap`: this is an
    /// ordered pair list, and sorting the keys here would break the
    /// serialized bytes.
    #[serde(
        default,
        rename = "methodReturns",
        skip_serializing_if = "OrderedMap::is_empty"
    )]
    pub method_returns: OrderedMap<String>,
    /// The extension methods this type declares, in source
    /// order, deduped by (name, thisType, arityMin, arityMax). Appended after
    /// `method_returns`, and omitted entirely when empty, so a type declaring
    /// none keeps its exact prior bytes.
    #[serde(
        default,
        rename = "extensionMethods",
        skip_serializing_if = "Vec::is_empty"
    )]
    pub extension_methods: Vec<FragExtensionMethod>,
    /// DIRECT base-type identifiers, source
    /// order, deduped. Appended LAST, after `extension_methods`, omitted when
    /// empty. A resolution input only: `resolve_graph` strips it (along with
    /// properties/fields/extensionMethods) before graph.json's def rows, so
    /// the on-disk def bytes are unchanged.
    #[serde(default, skip_serializing_if = "Vec::is_empty")]
    pub bases: Vec<String>,
    /// The declaring type's own type-parameter names, empty for
    /// every non-generic declaration. Appended after `bases`, omitted when
    /// empty. A resolution input, like `bases`: the ctor-DI resolver's
    /// "is this def itself an open-generic implementation" signal.
    #[serde(default, rename = "typeParams", skip_serializing_if = "Vec::is_empty")]
    pub type_params: Vec<String>,
    /// Per base name that carried a type-argument list, that
    /// list's generic-arg descriptors relative to `type_params` (`OrderedMap`
    /// for the same reason `method_returns` is one: the serialized key order
    /// is significant). Appended after `type_params`, omitted when
    /// empty.
    #[serde(
        default,
        rename = "baseGenericArgs",
        skip_serializing_if = "OrderedMap::is_empty"
    )]
    pub base_generic_args: OrderedMap<Vec<String>>,
    /// The methods a test framework would DISCOVER as
    /// tests, source order, deduped. Appended LAST, after `baseGenericArgs`,
    /// omitted when empty. Unlike its neighbours this one is NOT stripped by
    /// `resolve_graph`: it is what `devscout tests` answers from.
    #[serde(default, rename = "testMethods", skip_serializing_if = "Vec::is_empty")]
    pub test_methods: Vec<String>,
    /// Property name -> declared type fact, in source order and
    /// under the same dedup as `properties`. An `OrderedMap` for the same
    /// reason `method_returns` is one: the serialized key order is significant.
    /// Appended LAST, after `test_methods`, omitted when empty. A
    /// resolution input only, like `properties`/`fields`.
    #[serde(
        default,
        rename = "propertyTypes",
        skip_serializing_if = "OrderedMap::is_empty"
    )]
    pub property_types: OrderedMap<FragFact>,
    /// Field name -> declared type fact, in source order and
    /// under the same dedup as `fields`. Mirrors `propertyTypes` field for
    /// field: an `OrderedMap` for the same reason (the serialized key order
    /// is significant), a resolution input only, like `properties`/`fields`,
    /// and this is a purely additive field -- an absent key reads back as
    /// "no fields typed", the safe default for every fragment cached before
    /// this field existed, so it joins the schema with no cache-version
    /// bump. Appended right after `propertyTypes`, omitted when empty.
    #[serde(
        default,
        rename = "fieldTypes",
        skip_serializing_if = "OrderedMap::is_empty"
    )]
    pub field_types: OrderedMap<FragFact>,
    /// Per method name `methodReturns` also carries an entry for,
    /// that return type's top-level generic-arg descriptors -- the same
    /// capture `baseGenericArgs` keeps beside `bases` (see extract.rs's
    /// `DefRecord`). `methodReturns` itself is left exactly as it always
    /// was (the bare return-type identifier, "Task" for
    /// `Task<Order> GetAsync()`) so an UNAWAITED use of the same callee
    /// keeps reading "Task" unchanged; this is a purely additive sibling
    /// field, not a reshaping of `methodReturns`, which is what lets it
    /// join the schema with no cache-version bump -- an absent key reads
    /// back as "no generic args", the safe default for every fragment
    /// cached before this field existed. Appended LAST of all, after
    /// `fieldTypes`, omitted when empty.
    #[serde(
        default,
        rename = "methodReturnArgs",
        skip_serializing_if = "OrderedMap::is_empty"
    )]
    pub method_return_args: OrderedMap<Vec<String>>,
    /// Declared method names `methods` does not carry because
    /// `is_recorded_method` gates that list on a literal `public` modifier
    /// (or `kind == "interface"`, where this list is always empty). Source
    /// order, no dedup, same as `methods`. A resolution input only, like
    /// `properties`/`fields`/`bases`: `resolve_graph` strips it before
    /// graph.json's def rows. Consulted only for hierarchy-internal
    /// receivers (`base.` and the `this.` shape's own base walk); the
    /// scored tier keeps reading `methods` alone. Appended LAST of all,
    /// after `methodReturnArgs`, omitted when empty -- purely additive, so
    /// an absent key reads back as "no non-public methods", the safe
    /// default for every fragment cached before this field existed, which
    /// is what lets it join the schema with no cache-version bump.
    #[serde(
        default,
        rename = "nonPublicMethods",
        skip_serializing_if = "Vec::is_empty"
    )]
    pub non_public_methods: Vec<String>,
    /// Method name -> the (min, max) argument-count range every overload
    /// sharing that name accepts, one tuple per overload, in declaration
    /// order -- covers every method, public and non-public alike (see
    /// `extract::DefRecord::method_arities`). `max` is -1 for an unbounded
    /// `params` overload, the same sentinel `FragExtensionMethod::arity_max`
    /// already uses. An `OrderedMap` for the same reason `methodReturns` is
    /// one: the serialized key order is significant. Appended LAST of all,
    /// after `nonPublicMethods`, omitted when empty -- purely additive, so
    /// an absent key reads back as "no arity facts", the safe default for
    /// every fragment cached before this field existed, which is what lets
    /// it join the schema with no cache-version bump.
    #[serde(
        default,
        rename = "methodArities",
        skip_serializing_if = "OrderedMap::is_empty"
    )]
    pub method_arities: OrderedMap<Vec<(usize, i64)>>,
    /// Method name -> per-overload parameter type descriptors, one
    /// `Vec<String>` per overload in declaration order -- covers every
    /// method, public and non-public alike, same method set as
    /// `methodArities` (see `extract::DefRecord::method_params`). A
    /// position naming a type parameter of the enclosing method or class is
    /// recorded as `"*"`; a parameter carrying the `this` modifier is
    /// written `"this <descriptor>"`. A `delegate` def carries exactly one
    /// entry here, keyed `"Invoke"`. An `OrderedMap` for the same reason
    /// `methodArities` is one: the serialized key order is significant.
    /// Appended LAST of all, after `methodArities`, omitted when empty.
    /// Joined the schema with the v18 cache bump: a v17 fragment read back
    /// carries none, and every overload-shape/`this`-marker/callee-slot
    /// lookup this field backs would silently see no candidates.
    #[serde(
        default,
        rename = "methodParams",
        skip_serializing_if = "OrderedMap::is_empty"
    )]
    pub method_params: OrderedMap<Vec<Vec<String>>>,
    #[serde(default, rename = "endLine", skip_serializing_if = "is_zero")]
    /// The end line value.
    pub end_line: usize,
}

/// One declared type fact: the type NAME, plus its top-level
/// type-argument descriptors when the declaration carried any. Field order
/// (`type`, `args`) is significant, and `args` is omitted when absent.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct FragFact {
    #[serde(rename = "type")]
    /// The type name value.
    pub type_name: String,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    /// The args value.
    pub args: Option<Vec<String>>,
}

/// One `extensionMethods` entry. Serialized field order (`name`, `thisType`,
/// `arityMin`, `arityMax`, `thisArgs`) is significant, and serde emits struct
/// fields in declaration order. The two arity halves are NOT optional: they joined the
/// schema with the v6 cache rename, so no fragment this reader can meet is
/// missing them. `arity_max` is signed because -1 is the unbounded-`params`
/// sentinel.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct FragExtensionMethod {
    /// The name value.
    pub name: String,
    #[serde(rename = "thisType")]
    /// The this type value.
    pub this_type: String,
    #[serde(rename = "arityMin")]
    /// The arity min value.
    pub arity_min: usize,
    #[serde(rename = "arityMax")]
    /// The arity max value.
    pub arity_max: i64,
    /// Present only when the this-parameter type is generic (the key is omitted
    /// key otherwise), so a non-generic entry keeps four fields exactly.
    #[serde(default, rename = "thisArgs", skip_serializing_if = "Option::is_none")]
    pub this_args: Option<Vec<String>>,
}

/// One untyped lambda parameter's callee slot (see extract.rs's `LambdaSlot`).
///
/// Field order (`owner`, `member`, `argCount`, `argIndex`,
/// `arity`, `index`) is significant: serde emits struct fields in
/// declaration order under `#[serde(rename_all = "camelCase")]`.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct FragLambdaSlot {
    /// The callee's type-name text.
    pub owner: String,
    /// The callee method name.
    pub member: String,
    /// The argument count of the callee invocation.
    pub arg_count: usize,
    /// The position of the lambda among the callee invocation's arguments.
    pub arg_index: usize,
    /// The lambda's own parameter count.
    pub arity: usize,
    /// This parameter's position inside the lambda's parameter list.
    pub index: usize,
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
#[serde(untagged)]
/// Represents `FragUsing`.
pub enum FragUsing {
    /// The value value.
    Alias {
        /// The alias name.
        alias: String,
        /// The aliased target.
        target: String,
        /// Whether the directive is global.
        global: bool,
    },
    /// The value value.
    Plain {
        /// The imported namespace text.
        text: String,
        /// Whether the directive is global.
        global: bool,
    },
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
/// Represents `FragRef`.
pub struct FragRef {
    /// The kind value.
    pub kind: String,
    /// The name value.
    pub name: String,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    /// The qualified value.
    pub qualified: Option<String>,
    #[serde(default, skip_serializing_if = "Option::is_none")]
    /// The member value.
    pub member: Option<String>,
    /// The line value.
    pub line: usize,
    /// Always serialized, including when `null` (imports refs) -- NOT
    /// `skip_serializing_if`, unlike `qualified`/`member` which are omitted
    /// entirely when absent. See extract.rs's RefRecord doc comment.
    pub namespace: Option<String>,
    #[serde(
        default,
        rename = "typeArgCount",
        skip_serializing_if = "Option::is_none"
    )]
    /// The type arg count value.
    pub type_arg_count: Option<usize>,
    /// Type-certainty flag (see extract.rs's RefRecord). Serialized last and
    /// only when `true`; an absent key reads back as false, which also makes
    /// an older fragment JSON parse safely.
    #[serde(default, skip_serializing_if = "is_false")]
    pub generic: bool,
    /// Receiver fact (see extract.rs's RefRecord). Appended AFTER `generic`,
    /// and set only when a fact actually fired -- so it serializes last and
    /// only when present, and an absent key reads back as "no fact", the safe
    /// default.
    #[serde(
        default,
        rename = "receiverType",
        skip_serializing_if = "Option::is_none"
    )]
    pub receiver_type: Option<String>,
    /// The callee arg count (see extract.rs's RefRecord). Appended AFTER
    /// `receiverType`, set only when the member access was the callee of an
    /// invocation -- so it serializes last and only when present, and an
    /// absent key reads back as "not a call", which is what keeps a property
    /// read out of the extension tier.
    #[serde(default, rename = "argCount", skip_serializing_if = "Option::is_none")]
    pub arg_count: Option<usize>,
    /// Receiver generic-arg descriptors (see extract.rs's RefRecord). Appended
    /// LAST, after `argCount`, set only when the receiver's DECLARED type was
    /// generic -- an absent key reads back as "not generic", which is what
    /// makes a generic-vs-non-generic pairing fail to unify.
    #[serde(
        default,
        rename = "receiverArgs",
        skip_serializing_if = "Option::is_none"
    )]
    pub receiver_args: Option<Vec<String>>,
    /// Enclosing-type stack (see extract.rs's RefRecord). Appended LAST, after
    /// `receiverArgs`, and set only when non-empty. A Vec rather than an Option
    /// because empty and absent mean the same thing here -- a ref at namespace
    /// level and an older cached fragment both read back as "no enclosing
    /// type", which is what keeps them off the step.
    #[serde(default, rename = "outerTypes", skip_serializing_if = "Vec::is_empty")]
    pub outer_types: Vec<String>,
    /// Generic-arg descriptors for a 'ctor-param' ref (see extract.rs's
    /// RefRecord). Appended LAST of all, after `outerTypes`, and set only when
    /// the parameter's type was generic.
    #[serde(default, skip_serializing_if = "Option::is_none")]
    pub args: Option<Vec<String>>,
    /// (See extract.rs's RefRecord.) The type whose PROPERTY the
    /// qualifier's last segment is, for a two-segment chain whose head the
    /// enclosing scope could type. Appended after `args`, and never present
    /// alongside `receiverType`.
    #[serde(
        default,
        rename = "receiverPropertyOwner",
        skip_serializing_if = "Option::is_none"
    )]
    pub receiver_property_owner: Option<String>,
    /// (See extract.rs's RefRecord.) The type whose METHOD a
    /// `var x = Q.M(...)` initializer called, and that method's name. Appended
    /// LAST of all, always as a pair, and never alongside `receiverType`: an
    /// absent pair reads back as "no call fact", which is what leaves the local
    /// taken-but-unknown.
    #[serde(
        default,
        rename = "receiverCallOwner",
        skip_serializing_if = "Option::is_none"
    )]
    pub receiver_call_owner: Option<String>,
    #[serde(
        default,
        rename = "receiverCallMember",
        skip_serializing_if = "Option::is_none"
    )]
    /// The receiver call member value.
    pub receiver_call_member: Option<String>,
    /// `true` for a `base.` qualifier -- the member lookup starts at the
    /// enclosing type's bases and never considers the enclosing type
    /// itself (see `extract.rs`'s `RefRecord`). Appended LAST of all, and
    /// omitted when `false` -- an absent key reads back as `false`, the
    /// same as a plain `this.` receiver and as every ref kind that never
    /// sets it, and also what makes a v15 cached fragment parse safely.
    #[serde(default, rename = "receiverBase", skip_serializing_if = "is_false")]
    pub receiver_base: bool,
    /// `true` when `receiverCallOwner`/`receiverCallMember` came from an
    /// AWAITED call (see `extract.rs`'s `RefRecord`). Appended LAST of all,
    /// after `receiverBase`, and omitted when `false` -- an absent key reads
    /// back as `false`, the same as an unawaited call fact and as every ref
    /// kind that never sets it, which is also what lets a cached fragment
    /// from before this field existed parse safely with no cache-version
    /// bump: it simply reads back as "not awaited", the same answer the
    /// resolver gave before this field existed.
    #[serde(default, rename = "receiverAwaited", skip_serializing_if = "is_false")]
    pub receiver_awaited: bool,
    /// `true` when this ref's qualifier is a bare identifier for which the
    /// enclosing MEMBER's own fact table (locals, parameters, lambda
    /// parameters, patterns, `out` designations) holds ANY entry for the
    /// name, typed or taken-but-unknown (see `extract.rs`'s `RefRecord` and
    /// `Scope::has_local_fact`). Read ONLY by the bare-identifier
    /// field/property fallback: a member-scoped name always shadows a
    /// same-named field, whether or not anything vouches for its type, so
    /// that fallback never runs when this is `true`. `false` for every
    /// dotted or generic qualifier, for `this.`/`base.` (never asked of the
    /// enclosing scope's local table at all), and for every ref kind but
    /// `uses-member`. Appended LAST of all, after `receiverAwaited`, and
    /// omitted when `false` -- an absent key reads back as `false`, the
    /// same as every ref kind that never sets it, which is also what lets a
    /// cached fragment from before this field existed parse safely with no
    /// cache-version bump.
    #[serde(default, rename = "receiverLocal", skip_serializing_if = "is_false")]
    pub receiver_local: bool,
    /// Set when this ref's qualifier is an untyped lambda parameter whose
    /// type is a delegate parameter of some OTHER callee (see extract.rs's
    /// `RefRecord`). Never present alongside `receiverType` or
    /// `receiverCallOwner`. Appended LAST of all, after `receiverLocal`,
    /// omitted when absent. Joined the schema with the v18 cache bump: a
    /// v17 fragment read back carries none, and every untyped-lambda
    /// callee-slot lookup this field backs would silently see no
    /// candidate.
    #[serde(
        default,
        rename = "receiverLambda",
        skip_serializing_if = "Option::is_none"
    )]
    pub receiver_lambda: Option<FragLambdaSlot>,
}

fn is_false(b: &bool) -> bool {
    !*b
}

fn is_zero(n: &usize) -> bool {
    *n == 0
}

/// One declared member, with the line its own NAME token sits on.
/// Field order (`name`, `kind`, `line`, `owner`) is significant, and `owner`
/// is omitted when empty -- which is how
/// a markup or resource key, owned by no C# type, serializes with three fields.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
pub struct FragName {
    /// The name value.
    pub name: String,
    /// The kind value.
    pub kind: String,
    /// The line value.
    pub line: usize,
    #[serde(default, skip_serializing_if = "String::is_empty")]
    /// The owner value.
    pub owner: String,
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
/// Represents `Fragment`.
pub struct Fragment {
    /// The defs value.
    pub defs: Vec<FragDef>,
    /// The usings value.
    pub usings: Vec<FragUsing>,
    /// The refs value.
    pub refs: Vec<FragRef>,
    /// Appended LAST, after `refs`. Always serialized, like its
    /// three siblings: a fragment's top-level arrays are a fixed shape, and
    /// only the fields INSIDE a record follow the omit-when-empty rule.
    #[serde(default)]
    pub names: Vec<FragName>,
}

/// The two shapes a cached fragment can have. Each rel is keyed to whichever
/// shape the file's grammar produced; the `ts: 1` tag is what tells them
/// apart, on disk and at the
/// resolver's door. Untagged, and TS FIRST: a C#/markup fragment carries no
/// `ts` key (so the TS arm always fails on it) and a TS fragment carries no
/// `usings` (so the C# arm always fails on it) -- the discrimination is total
/// in both directions, never a first-match-wins guess.
#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
#[serde(untagged)]
pub enum AnyFragment {
    /// Represents `Ts`.
    Ts(extract::TsFragment),
    /// Represents `Cs`.
    Cs(Fragment),
}

impl From<Fragment> for AnyFragment {
    fn from(f: Fragment) -> Self {
        AnyFragment::Cs(f)
    }
}

impl From<extract::TsFragment> for AnyFragment {
    fn from(f: extract::TsFragment) -> Self {
        AnyFragment::Ts(f)
    }
}

/// Build a graph fragment from this crate's extractor output.
/// `Extraction.purpose` has no fragment
/// counterpart -- the fragment is graph-only.
#[allow(
    clippy::too_many_lines,
    reason = "one ordered field-by-field translation from Extraction into Fragment; splitting it would separate fields that must stay mapped consistently"
)]
pub fn fragment_from_extraction(e: &extract::Extraction) -> Fragment {
    Fragment {
        defs: e
            .defs
            .iter()
            .map(|d| FragDef {
                id: d.id.clone(),
                name: d.name.clone(),
                namespace: d.namespace.clone(),
                kind: d.kind.clone(),
                line: d.line,
                methods: d.methods.clone(),
                properties: d.properties.clone(),
                fields: d.fields.clone(),
                method_returns: {
                    let mut m = OrderedMap::new();
                    for (name, returns) in &d.method_returns {
                        m.insert(name.clone(), returns.clone());
                    }
                    m
                },
                extension_methods: d
                    .extension_methods
                    .iter()
                    .map(|e| FragExtensionMethod {
                        name: e.name.clone(),
                        this_type: e.this_type.clone(),
                        arity_min: e.arity_min,
                        arity_max: e.arity_max,
                        this_args: e.this_args.clone(),
                    })
                    .collect(),
                bases: d.bases.clone(),
                type_params: d.type_params.clone(),
                base_generic_args: {
                    let mut m = OrderedMap::new();
                    for (name, args) in &d.base_generic_args {
                        m.insert(name.clone(), args.clone());
                    }
                    m
                },
                test_methods: d.test_methods.clone(),
                property_types: {
                    let mut m = OrderedMap::new();
                    for (name, fact) in &d.property_types {
                        m.insert(
                            name.clone(),
                            FragFact {
                                type_name: fact.type_name.clone(),
                                args: fact.args.clone(),
                            },
                        );
                    }
                    m
                },
                field_types: {
                    let mut m = OrderedMap::new();
                    for (name, fact) in &d.field_types {
                        m.insert(
                            name.clone(),
                            FragFact {
                                type_name: fact.type_name.clone(),
                                args: fact.args.clone(),
                            },
                        );
                    }
                    m
                },
                method_return_args: {
                    let mut m = OrderedMap::new();
                    for (name, args) in &d.method_return_args {
                        m.insert(name.clone(), args.clone());
                    }
                    m
                },
                non_public_methods: d.non_public_methods.clone(),
                method_arities: {
                    let mut m = OrderedMap::new();
                    for (name, ranges) in &d.method_arities {
                        m.insert(name.clone(), ranges.clone());
                    }
                    m
                },
                method_params: {
                    let mut m = OrderedMap::new();
                    for (name, overloads) in &d.method_params {
                        m.insert(name.clone(), overloads.clone());
                    }
                    m
                },
                end_line: d.end_line,
            })
            .collect(),
        usings: e
            .usings
            .iter()
            .map(|u| match u {
                extract::UsingRecord::Alias {
                    alias,
                    target,
                    global,
                } => FragUsing::Alias {
                    alias: alias.clone(),
                    target: target.clone(),
                    global: *global,
                },
                extract::UsingRecord::Plain { text, global } => FragUsing::Plain {
                    text: text.clone(),
                    global: *global,
                },
            })
            .collect(),
        refs: e
            .refs
            .iter()
            .map(|r| FragRef {
                kind: r.kind.clone(),
                name: r.name.clone(),
                qualified: r.qualified.clone(),
                member: r.member.clone(),
                line: r.line,
                namespace: r.namespace.clone(),
                type_arg_count: r.type_arg_count,
                generic: r.generic,
                receiver_type: r.receiver_type.clone(),
                arg_count: r.arg_count,
                receiver_args: r.receiver_args.clone(),
                outer_types: r.outer_types.clone(),
                args: r.args.clone(),
                receiver_property_owner: r.receiver_property_owner.clone(),
                receiver_call_owner: r.receiver_call_owner.clone(),
                receiver_call_member: r.receiver_call_member.clone(),
                receiver_base: r.receiver_base,
                receiver_awaited: r.receiver_awaited,
                receiver_local: r.receiver_local,
                receiver_lambda: r.receiver_lambda.as_ref().map(|s| FragLambdaSlot {
                    owner: s.owner.clone(),
                    member: s.member.clone(),
                    arg_count: s.arg_count,
                    arg_index: s.arg_index,
                    arity: s.arity,
                    index: s.index,
                }),
            })
            .collect(),
        names: e
            .names
            .iter()
            .map(|n| FragName {
                name: n.name.clone(),
                kind: n.kind.clone(),
                line: n.line,
                owner: n.owner.clone(),
            })
            .collect(),
    }
}

/// Markup and resource files never reach the extractor: a
/// line scan reads them instead (see markup.rs). They still get a fragment even
/// when they declare nothing, because the fragments index is what tells `map`
/// whether the graph's input set changed, and a file missing from it reads as a
/// permanent mismatch. `usings` is always empty: XAML has no using-directive
/// equivalent, and the `xmlns:` prefix declarations that stand in for one are
/// already resolved into fully-qualified ref names by the scan.
pub fn markup_fragment(root: &Path, rel: &str) -> Option<Fragment> {
    // Lossy read: an invalid byte becomes U+FFFD rather than dropping the
    // file.
    let text = String::from_utf8_lossy(&fs::read(root.join(rel)).ok()?).into_owned();
    let facts = crate::markup::markup_facts(rel, &text);
    Some(Fragment {
        defs: facts
            .defs
            .into_iter()
            .map(|d| FragDef {
                id: d.id,
                name: d.name,
                namespace: d.namespace,
                kind: d.kind,
                line: d.line,
                methods: Vec::new(),
                properties: Vec::new(),
                fields: Vec::new(),
                method_returns: OrderedMap::new(),
                extension_methods: Vec::new(),
                bases: Vec::new(),
                type_params: Vec::new(),
                base_generic_args: OrderedMap::new(),
                test_methods: Vec::new(),
                property_types: OrderedMap::new(),
                field_types: OrderedMap::new(),
                method_return_args: OrderedMap::new(),
                non_public_methods: Vec::new(),
                method_arities: OrderedMap::new(),
                method_params: OrderedMap::new(),
                end_line: d.line,
            })
            .collect(),
        usings: Vec::new(),
        refs: facts
            .refs
            .into_iter()
            .map(|r| FragRef {
                kind: r.kind,
                name: r.name,
                qualified: r.qualified,
                member: r.member,
                line: r.line,
                // A markup ref site has no enclosing namespace of its own, and
                // the empty string is what a C# ref at file scope carries too --
                // never `None`, which is the 'imports' spelling.
                namespace: Some(String::new()),
                type_arg_count: Some(0),
                generic: false,
                receiver_type: None,
                arg_count: None,
                receiver_args: None,
                outer_types: Vec::new(),
                args: None,
                receiver_property_owner: None,
                receiver_call_owner: None,
                receiver_call_member: None,
                receiver_base: false,
                receiver_awaited: false,
                receiver_local: false,
                receiver_lambda: None,
            })
            .collect(),
        names: facts
            .names
            .into_iter()
            .map(|n| FragName {
                name: n.name,
                kind: n.kind,
                line: n.line,
                owner: n.owner,
            })
            .collect(),
    })
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
/// Represents `FragmentCacheEntry`.
pub struct FragmentCacheEntry {
    /// The mtime value.
    pub mtime: i64,
    /// The fragment value.
    pub fragment: AnyFragment,
}

fn read_fragments_cache(root: &Path) -> OrderedMap<FragmentCacheEntry> {
    match fs::read_to_string(fragments_cache_path(root)) {
        Ok(text) => serde_json::from_str(&text).unwrap_or_default(),
        Err(_) => OrderedMap::default(),
    }
}

fn write_fragments_cache(root: &Path, cache: &OrderedMap<FragmentCacheEntry>) -> io::Result<()> {
    atomic_write_json(&fragments_cache_path(root), cache)
}

/// Read the fragments index (rel -> mtime). Used for the per-file reuse
/// decision, independent of the graph rebuild.
pub fn read_fragments_index(root: &Path) -> OrderedMap<i64> {
    match fs::read_to_string(fragments_index_path(root)) {
        Ok(text) => serde_json::from_str(&text).unwrap_or_default(),
        Err(_) => OrderedMap::default(),
    }
}

fn write_fragments_index(root: &Path, cache: &OrderedMap<FragmentCacheEntry>) -> io::Result<()> {
    let mut index = OrderedMap::new();
    for (rel, entry) in cache.iter() {
        index.insert(rel.clone(), entry.mtime);
    }
    atomic_write_json(&fragments_index_path(root), &index)
}

/// Whether the fragments index is stale for the given graph files (any mtime
/// mismatch, or a differing file count).
pub fn index_is_stale(index: &OrderedMap<i64>, graph_files: &[GraphFile]) -> bool {
    graph_files
        .iter()
        .any(|f| index.get(&f.rel) != Some(&f.mtime))
        || index.len() != graph_files.len()
}

// ---------------------------------------------------------------------------
// `devscout map`'s cache-then-resolve-then-write cycle.
// ---------------------------------------------------------------------------

/// One file that contributes a graph fragment: C# (defs, refs, member names),
/// markup (`x:Class`/`x:Name`, `.resw` keys -- names only) or TS/JS
/// (imports, exported declarations, call/JSX/dispatch references).
#[derive(Debug, Clone)]
pub struct GraphFile {
    /// The rel value.
    pub rel: String,
    /// The mtime value.
    pub mtime: i64,
}

#[derive(Debug)]
/// Represents `RebuildOutcome`.
pub enum RebuildOutcome {
    /// Represents `NotRebuilt`.
    NotRebuilt,
    /// Represents `Rebuilt`.
    Rebuilt(Graph),
}

/// Whether the graph.json already on disk was written at the CURRENT schema
/// version. Reads the first 64 bytes and compares the literal
/// `{"schema_version":N,` prefix rather than deserializing: `schema_version`
/// is the first key `Graph` serializes, the artifact can be tens of
/// megabytes, and this runs on the fast path whose whole point is not opening
/// it. Anything else -- an older version, an unreadable or truncated file --
/// answers false and costs a rebuild, which is the safe direction.
fn graph_schema_is_current(root: &Path) -> bool {
    let Ok(mut file) = fs::File::open(graph_json_path(root)) else {
        return false;
    };
    let mut head = [0u8; 64];
    let mut filled = 0;
    while filled < head.len() {
        match file.read(&mut head[filled..]) {
            Ok(0) => break,
            Ok(n) => filled += n,
            Err(_) => return false,
        }
    }
    head[..filled].starts_with(format!("{{\"schema_version\":{GRAPH_SCHEMA_VERSION},").as_bytes())
}

// Mirrors the model's units into the staleness sidecar. No model means the
// repo declares no `.csproj`, and then the file must NOT exist: an empty
// `[]` left behind would be indistinguishable from "no model" on the read
// side, and the sidecar's whole job is telling those two apart.
fn write_project_units(
    root: &Path,
    model: Option<&crate::project::ProjectModel>,
) -> io::Result<()> {
    match model {
        Some(m) => atomic_write_json(&project_units_path(root), &crate::project::graph_units(m)),
        None => {
            let path = project_units_path(root);
            match fs::remove_file(&path) {
                Ok(()) => Ok(()),
                Err(e) if e.kind() == io::ErrorKind::NotFound => Ok(()),
                Err(e) => Err(e),
            }
        }
    }
}

/// `fresh_fragments`: fragments this run's extractor produced for files that
/// needed reparsing (the same set that got a fresh purpose signature in the
/// real `devscout map` flow -- `mapcmd::map_repo` assembles it). `changed`: from the
/// caller's own `indexIsStale`-equivalent check against `csFiles`, passed in
/// rather than recomputed so the unchanged path never opens any graph file.
/// `model`: the repo's discovered `.csproj` projects, or `None` when it
/// declares none -- serialized into `graph.units` and mirrored into the
/// `project_units_path` staleness sidecar. The caller is expected to have
/// already folded `project::sidecar_differs` into `changed`; this function
/// only writes the sidecar, it never decides on it.
pub fn rebuild_graph(
    root: &Path,
    graph_files: &[GraphFile],
    fresh_fragments: &HashMap<String, AnyFragment>,
    changed: bool,
    model: Option<&crate::project::ProjectModel>,
) -> io::Result<RebuildOutcome> {
    if !changed && graph_json_path(root).exists() && graph_schema_is_current(root) {
        return Ok(RebuildOutcome::NotRebuilt);
    }

    let cache = read_fragments_cache(root);
    // Split at the door: the two shapes share no field beyond
    // `defs`, and letting one resolver see the other's names would resolve a
    // C# type reference onto a same-named TypeScript const. Built as two vecs
    // here rather than one mixed vec split later so no fragment is cloned a
    // third time on the rebuild path.
    let mut merged_cs: Vec<(String, Fragment)> = Vec::new();
    let mut merged_ts: Vec<(String, extract::TsFragment)> = Vec::new();
    let mut new_cache: OrderedMap<FragmentCacheEntry> = OrderedMap::new();
    for f in graph_files {
        let fragment = match cache.get(&f.rel) {
            Some(entry) if entry.mtime == f.mtime => Some(entry.fragment.clone()),
            _ => fresh_fragments.get(&f.rel).cloned(),
        };
        let Some(fragment) = fragment else { continue };
        match &fragment {
            AnyFragment::Cs(c) => merged_cs.push((f.rel.clone(), c.clone())),
            AnyFragment::Ts(t) => merged_ts.push((f.rel.clone(), t.clone())),
        }
        new_cache.insert(
            f.rel.clone(),
            FragmentCacheEntry {
                mtime: f.mtime,
                fragment,
            },
        );
    }

    let graph = crate::resolve::resolve_graph_with_model(root, &merged_cs, &merged_ts, model);
    write_graph(root, &graph)?;
    write_project_units(root, model)?;
    write_fragments_cache(root, &new_cache)?;
    write_fragments_index(root, &new_cache)?;
    remove_superseded_caches(root);
    Ok(RebuildOutcome::Rebuilt(graph))
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::time::{SystemTime, UNIX_EPOCH};

    fn temp_dir(label: &str) -> PathBuf {
        let nanos = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap()
            .as_nanos();
        let dir = std::env::temp_dir().join(format!("scout-graph-test-{label}-{nanos}"));
        fs::create_dir_all(&dir).unwrap();
        dir
    }

    // --- OrderedMap: order + round-trip -------------------------------

    #[test]
    fn ordered_map_preserves_insertion_order_through_json_round_trip() {
        let mut m: OrderedMap<i64> = OrderedMap::new();
        m.insert("z.cs".to_string(), 3);
        m.insert("a.cs".to_string(), 1);
        m.insert("m.cs".to_string(), 2);
        let json = serde_json::to_string(&m).unwrap();
        assert_eq!(json, r#"{"z.cs":3,"a.cs":1,"m.cs":2}"#);

        let reparsed: OrderedMap<i64> = serde_json::from_str(&json).unwrap();
        let keys: Vec<&String> = reparsed.iter().map(|(k, _)| k).collect();
        assert_eq!(keys, vec!["z.cs", "a.cs", "m.cs"]);
    }

    #[test]
    fn ordered_map_insert_overwrite_keeps_original_position() {
        let mut m: OrderedMap<i64> = OrderedMap::new();
        m.insert("a".to_string(), 1);
        m.insert("b".to_string(), 2);
        m.insert("a".to_string(), 99);
        let keys: Vec<&String> = m.iter().map(|(k, _)| k).collect();
        assert_eq!(keys, vec!["a", "b"]);
        assert_eq!(m.get("a"), Some(&99));
    }

    // --- Percent1: number-shaped formatting -------------------------

    #[test]
    fn percent1_whole_value_serializes_without_decimal_point() {
        let p = Percent1::from_ratio(2, 10); // 20.0 -> "20"
        assert_eq!(serde_json::to_string(&p).unwrap(), "20");
    }

    #[test]
    fn percent1_fractional_value_serializes_with_one_decimal_digit() {
        let p = Percent1::from_ratio(1, 3); // 33.333... -> round to 33.3
        assert_eq!(serde_json::to_string(&p).unwrap(), "33.3");
    }

    #[test]
    fn percent1_zero_denominator_is_zero() {
        assert_eq!(Percent1::from_ratio(0, 0), Percent1::zero());
        assert_eq!(serde_json::to_string(&Percent1::zero()).unwrap(), "0");
    }

    // --- FragDef's new keys, appended last, omitted when empty ----------------------

    fn frag_def(
        methods: &[&str],
        properties: &[&str],
        fields: &[&str],
        method_returns: &[(&str, &str)],
        extension_methods: &[(&str, &str, usize, i64)],
    ) -> FragDef {
        frag_def_with_bases(
            methods,
            properties,
            fields,
            method_returns,
            extension_methods,
            &[],
        )
    }

    fn frag_def_with_bases(
        methods: &[&str],
        properties: &[&str],
        fields: &[&str],
        method_returns: &[(&str, &str)],
        extension_methods: &[(&str, &str, usize, i64)],
        bases: &[&str],
    ) -> FragDef {
        let mut mr = OrderedMap::new();
        for (k, v) in method_returns {
            mr.insert((*k).to_string(), (*v).to_string());
        }
        FragDef {
            id: "App.Facts.Widget".into(),
            name: "Widget".into(),
            namespace: "App.Facts".into(),
            kind: "class".into(),
            line: 3,
            methods: methods.iter().map(|s| s.to_string()).collect(),
            properties: properties.iter().map(|s| s.to_string()).collect(),
            fields: fields.iter().map(|s| s.to_string()).collect(),
            method_returns: mr,
            extension_methods: extension_methods
                .iter()
                .map(|(n, t, lo, hi)| FragExtensionMethod {
                    name: (*n).to_string(),
                    this_type: (*t).to_string(),
                    arity_min: *lo,
                    arity_max: *hi,
                    this_args: None,
                })
                .collect(),
            bases: bases.iter().map(|s| s.to_string()).collect(),
            type_params: Vec::new(),
            base_generic_args: OrderedMap::new(),
            property_types: OrderedMap::new(),
            field_types: OrderedMap::new(),
            method_return_args: OrderedMap::new(),
            non_public_methods: Vec::new(),
            method_arities: OrderedMap::new(),
            method_params: OrderedMap::new(),
            test_methods: Vec::new(),
            end_line: 0,
        }
    }

    #[test]
    fn frag_def_appends_properties_fields_and_method_returns_last_in_that_order() {
        let json = serde_json::to_string(&frag_def(
            &["GetAsync"],
            &["Prefix"],
            &["_log"],
            &[("GetAsync", "Task")],
            &[],
        ))
        .unwrap();
        assert_eq!(
            json,
            r#"{"id":"App.Facts.Widget","name":"Widget","namespace":"App.Facts","kind":"class","line":3,"methods":["GetAsync"],"properties":["Prefix"],"fields":["_log"],"methodReturns":{"GetAsync":"Task"}}"#
        );
    }

    #[test]
    fn frag_def_omits_all_three_new_keys_when_the_type_declares_none_of_them() {
        let json = serde_json::to_string(&frag_def(&["Go"], &[], &[], &[], &[])).unwrap();
        assert_eq!(
            json,
            r#"{"id":"App.Facts.Widget","name":"Widget","namespace":"App.Facts","kind":"class","line":3,"methods":["Go"]}"#,
            "pre-stage-2 bytes preserved exactly"
        );
    }

    // --- extensionMethods lands AFTER methodReturns, entry keys
    // in (name, thisType, arityMin, arityMax, thisArgs) order, omitted when
    // empty; `bases` lands after extensionMethods -------------------------

    #[test]
    fn frag_def_appends_extension_methods_after_method_returns_with_the_arity_range_last() {
        let json = serde_json::to_string(&frag_def(
            &["Go"],
            &["Prefix"],
            &["_log"],
            &[("Go", "Task")],
            &[
                ("Render", "Widget", 0, 0),
                ("Render", "Widget", 2, 3),
                ("Trim", "string", 0, -1),
            ],
        ))
        .unwrap();
        assert_eq!(
            json,
            r#"{"id":"App.Facts.Widget","name":"Widget","namespace":"App.Facts","kind":"class","line":3,"methods":["Go"],"properties":["Prefix"],"fields":["_log"],"methodReturns":{"Go":"Task"},"extensionMethods":[{"name":"Render","thisType":"Widget","arityMin":0,"arityMax":0},{"name":"Render","thisType":"Widget","arityMin":2,"arityMax":3},{"name":"Trim","thisType":"string","arityMin":0,"arityMax":-1}]}"#
        );
    }

    #[test]
    fn frag_def_this_args_lands_after_arity_max_and_bases_after_extension_methods() {
        let mut d = frag_def_with_bases(
            &["Go"],
            &[],
            &[],
            &[],
            &[("Each", "List", 0, 0)],
            &["BaseWidget", "IWidget"],
        );
        d.extension_methods[0].this_args = Some(vec!["Widget".into()]);
        let json = serde_json::to_string(&d).unwrap();
        assert_eq!(
            json,
            r#"{"id":"App.Facts.Widget","name":"Widget","namespace":"App.Facts","kind":"class","line":3,"methods":["Go"],"extensionMethods":[{"name":"Each","thisType":"List","arityMin":0,"arityMax":0,"thisArgs":["Widget"]}],"bases":["BaseWidget","IWidget"]}"#
        );
        let reparsed: FragDef = serde_json::from_str(&json).unwrap();
        assert_eq!(
            reparsed.bases,
            vec!["BaseWidget".to_string(), "IWidget".to_string()]
        );
        assert_eq!(
            reparsed.extension_methods[0].this_args,
            Some(vec!["Widget".to_string()])
        );
    }

    #[test]
    fn frag_def_omits_bases_when_the_type_lists_none() {
        let json = serde_json::to_string(&frag_def(&["Go"], &[], &[], &[], &[])).unwrap();
        assert!(
            !json.contains("bases"),
            "an empty base list must be omitted entirely: {json}"
        );
        let reparsed: FragDef = serde_json::from_str(&json).unwrap();
        assert!(
            reparsed.bases.is_empty(),
            "an absent key reads back as \"lists none\""
        );
    }

    // --- test-coverage stage: testMethods lands AFTER bases, omitted when
    // the type declares no tests ------------------------------------------

    #[test]
    fn frag_def_appends_test_methods_last_after_bases() {
        let mut d = frag_def_with_bases(&["Go"], &[], &[], &[], &[], &["BaseWidget"]);
        d.test_methods = vec!["TotalsAnEmptyOrder".into(), "TotalsALineItem".into()];
        let json = serde_json::to_string(&d).unwrap();
        assert_eq!(
            json,
            r#"{"id":"App.Facts.Widget","name":"Widget","namespace":"App.Facts","kind":"class","line":3,"methods":["Go"],"bases":["BaseWidget"],"testMethods":["TotalsAnEmptyOrder","TotalsALineItem"]}"#
        );
        let reparsed: FragDef = serde_json::from_str(&json).unwrap();
        assert_eq!(
            reparsed.test_methods,
            vec![
                "TotalsAnEmptyOrder".to_string(),
                "TotalsALineItem".to_string()
            ]
        );
    }

    #[test]
    fn frag_def_omits_test_methods_when_the_type_declares_no_tests() {
        let json = serde_json::to_string(&frag_def(&["Go"], &[], &[], &[], &[])).unwrap();
        assert!(
            !json.contains("testMethods"),
            "pre-stage bytes preserved exactly: {json}"
        );
        let reparsed: FragDef = serde_json::from_str(&json).unwrap();
        assert!(
            reparsed.test_methods.is_empty(),
            "an absent key reads back as \"declares no tests\""
        );
    }

    #[test]
    fn frag_def_omits_extension_methods_when_the_type_declares_none() {
        let json =
            serde_json::to_string(&frag_def(&["Go"], &[], &[], &[("Go", "Task")], &[])).unwrap();
        assert!(
            !json.contains("extensionMethods"),
            "pre-stage-3 bytes preserved exactly: {json}"
        );
        let reparsed: FragDef = serde_json::from_str(&json).unwrap();
        assert!(
            reparsed.extension_methods.is_empty(),
            "an absent key reads back as \"declares none\""
        );
    }

    #[test]
    fn frag_def_method_returns_serializes_in_first_declaration_order_not_sorted() {
        // A BTreeMap here would emit Alpha before Zebra -- the required order
        // is insertion (first-declaration) order.
        let json = serde_json::to_string(&frag_def(
            &[],
            &[],
            &[],
            &[("Zebra", "Z"), ("Alpha", "A")],
            &[],
        ))
        .unwrap();
        assert!(
            json.ends_with(r#""methodReturns":{"Zebra":"Z","Alpha":"A"}}"#),
            "insertion order, not sorted: {json}"
        );
        let reparsed: FragDef = serde_json::from_str(&json).unwrap();
        let keys: Vec<&String> = reparsed.method_returns.iter().map(|(k, _)| k).collect();
        assert_eq!(
            keys,
            vec!["Zebra", "Alpha"],
            "and the order survives a round trip"
        );
    }

    // --- propertyTypes lands AFTER testMethods, omitted when the
    // type declares no typed property ---------------------------------------

    #[test]
    fn frag_def_appends_property_types_last_after_test_methods() {
        let mut d =
            frag_def_with_bases(&["Go"], &["Dial", "Slots"], &[], &[], &[], &["BaseWidget"]);
        d.test_methods = vec!["TotalsALineItem".into()];
        d.property_types.insert(
            "Dial".into(),
            FragFact {
                type_name: "Gauge".into(),
                args: None,
            },
        );
        d.property_types.insert(
            "Slots".into(),
            FragFact {
                type_name: "Toolbox".into(),
                args: Some(vec!["Gadget".into()]),
            },
        );
        let json = serde_json::to_string(&d).unwrap();
        assert_eq!(
            json,
            r#"{"id":"App.Facts.Widget","name":"Widget","namespace":"App.Facts","kind":"class","line":3,"methods":["Go"],"properties":["Dial","Slots"],"bases":["BaseWidget"],"testMethods":["TotalsALineItem"],"propertyTypes":{"Dial":{"type":"Gauge"},"Slots":{"type":"Toolbox","args":["Gadget"]}}}"#
        );
        let reparsed: FragDef = serde_json::from_str(&json).unwrap();
        let keys: Vec<&String> = reparsed.property_types.iter().map(|(k, _)| k).collect();
        assert_eq!(
            keys,
            vec!["Dial", "Slots"],
            "source order survives a round trip, like methodReturns"
        );
    }

    #[test]
    fn frag_def_omits_property_types_when_no_property_carries_a_fact() {
        let json = serde_json::to_string(&frag_def(&["Go"], &["Label"], &[], &[], &[])).unwrap();
        assert!(
            !json.contains("propertyTypes"),
            "pre-propertyTypes bytes preserved exactly: {json}"
        );
        let reparsed: FragDef = serde_json::from_str(&json).unwrap();
        assert!(
            reparsed.property_types.is_empty(),
            "an absent key reads back as \"no property vouches for a type\""
        );
    }

    // --- FragRef's receiverType then argCount, appended
    // after generic in that order ------------------------------------------

    fn frag_ref(generic: bool, receiver_type: Option<&str>, arg_count: Option<usize>) -> FragRef {
        FragRef {
            kind: "uses-member".into(),
            name: "repo".into(),
            qualified: None,
            member: Some("Save".into()),
            line: 7,
            namespace: Some("App.Shape".into()),
            type_arg_count: None,
            generic,
            receiver_type: receiver_type.map(String::from),
            arg_count,
            receiver_args: None,
            outer_types: Vec::new(),
            args: None,
            receiver_property_owner: None,
            receiver_call_owner: None,
            receiver_call_member: None,
            receiver_base: false,
            receiver_awaited: false,
            receiver_local: false,
            receiver_lambda: None,
        }
    }

    #[test]
    fn frag_ref_receiver_args_is_appended_last_after_arg_count() {
        let r = FragRef {
            receiver_args: Some(vec!["FutureState".into(), "*".into()]),
            ..frag_ref(false, Some("Binder"), Some(1))
        };
        let json = serde_json::to_string(&r).unwrap();
        assert_eq!(
            json,
            r#"{"kind":"uses-member","name":"repo","member":"Save","line":7,"namespace":"App.Shape","receiverType":"Binder","argCount":1,"receiverArgs":["FutureState","*"]}"#
        );
        let reparsed: FragRef = serde_json::from_str(&json).unwrap();
        assert_eq!(
            reparsed.receiver_args,
            Some(vec!["FutureState".to_string(), "*".to_string()])
        );
    }

    #[test]
    fn frag_ref_receiver_type_then_arg_count_are_appended_last_after_generic() {
        let json = serde_json::to_string(&frag_ref(true, Some("IRepo"), Some(2))).unwrap();
        assert_eq!(
            json,
            r#"{"kind":"uses-member","name":"repo","member":"Save","line":7,"namespace":"App.Shape","generic":true,"receiverType":"IRepo","argCount":2}"#
        );
    }

    #[test]
    fn frag_ref_arg_count_zero_still_serializes_it() {
        // The guard is presence (argCount may be 0), never truthiness -- a
        // zero-argument call is a real call and its 0 is what matches an
        // arity-0 extension.
        let json = serde_json::to_string(&frag_ref(false, Some("IRepo"), Some(0))).unwrap();
        assert!(
            json.ends_with(r#""receiverType":"IRepo","argCount":0}"#),
            "argCount 0 must survive: {json}"
        );
    }

    #[test]
    fn frag_ref_without_a_fact_keeps_its_pre_stage_2_bytes() {
        let json = serde_json::to_string(&frag_ref(false, None, None)).unwrap();
        assert_eq!(
            json,
            r#"{"kind":"uses-member","name":"repo","member":"Save","line":7,"namespace":"App.Shape"}"#
        );
        let reparsed: FragRef = serde_json::from_str(&json).unwrap();
        assert_eq!(
            reparsed.receiver_type, None,
            "an absent key reads back as no fact"
        );
        assert_eq!(
            reparsed.arg_count, None,
            "and an absent argCount reads back as \"not a call\""
        );
        assert_eq!(
            reparsed.receiver_args, None,
            "and an absent receiverArgs reads back as \"not generic\""
        );
    }

    // --- Def: also_in omission ------------------------------------------

    #[test]
    fn def_without_also_in_omits_the_key() {
        let d = Def {
            id: "Ns.Type".into(),
            name: "Type".into(),
            namespace: "Ns".into(),
            kind: "class".into(),
            file: "Ns/Type.cs".into(),
            line: 3,
            methods: vec![],
            test_methods: vec![],
            also_in: vec![],
            end_line: 0,
        };
        let json = serde_json::to_string(&d).unwrap();
        assert!(
            !json.contains("also_in"),
            "empty also_in must be omitted: {json}"
        );
    }

    #[test]
    fn def_end_line_serializes_last_and_defaults_when_absent() {
        let mut d = Def {
            id: "Ns.Type".into(),
            name: "Type".into(),
            namespace: "Ns".into(),
            kind: "class".into(),
            file: "Ns/Type.cs".into(),
            line: 3,
            methods: vec![],
            test_methods: vec![],
            also_in: vec![],
            end_line: 0,
        };
        assert!(!serde_json::to_string(&d).unwrap().contains("endLine"));
        d.end_line = 9;
        assert!(serde_json::to_string(&d)
            .unwrap()
            .ends_with(",\"endLine\":9}"));
    }

    #[test]
    fn def_with_also_in_includes_it_after_methods() {
        let d = Def {
            id: "Ns.Type".into(),
            name: "Type".into(),
            namespace: "Ns".into(),
            kind: "class".into(),
            file: "Ns/Type.cs".into(),
            line: 3,
            methods: vec!["M".into()],
            test_methods: vec![],
            also_in: vec![AlsoIn {
                file: "Ns/Type.Extra.cs".into(),
                line: 5,
            }],
            end_line: 0,
        };
        let json = serde_json::to_string(&d).unwrap();
        let methods_pos = json.find("\"methods\"").unwrap();
        let also_in_pos = json.find("\"also_in\"").unwrap();
        assert!(
            methods_pos < also_in_pos,
            "also_in must come after methods: {json}"
        );
    }

    // --- test-coverage stage: the def ROW keeps testMethods, between
    // methods and also_in ---------------------------------------------------

    #[test]
    fn def_row_places_test_methods_between_methods_and_also_in() {
        let d = Def {
            id: "Ns.TypeTests".into(),
            name: "TypeTests".into(),
            namespace: "Ns".into(),
            kind: "class".into(),
            file: "Ns/TypeTests.cs".into(),
            line: 3,
            methods: vec!["M".into()],
            test_methods: vec!["Fact1".into()],
            also_in: vec![AlsoIn {
                file: "Ns/TypeTests.Extra.cs".into(),
                line: 5,
            }],
            end_line: 0,
        };
        let json = serde_json::to_string(&d).unwrap();
        assert_eq!(
            json,
            r#"{"id":"Ns.TypeTests","name":"TypeTests","namespace":"Ns","kind":"class","file":"Ns/TypeTests.cs","line":3,"methods":["M"],"testMethods":["Fact1"],"also_in":[{"file":"Ns/TypeTests.Extra.cs","line":5}]}"#
        );
    }

    #[test]
    fn def_row_omits_test_methods_when_the_def_declares_no_tests() {
        let d = Def {
            id: "Ns.Type".into(),
            name: "Type".into(),
            namespace: "Ns".into(),
            kind: "class".into(),
            file: "Ns/Type.cs".into(),
            line: 3,
            methods: vec!["M".into()],
            test_methods: vec![],
            also_in: vec![],
            end_line: 0,
        };
        let json = serde_json::to_string(&d).unwrap();
        assert!(
            !json.contains("testMethods"),
            "empty testMethods must be omitted: {json}"
        );
    }

    // --- test-coverage stage: stats gains test_def_count, LAST -------------

    #[test]
    fn stats_appends_test_def_count_last_and_always_writes_it() {
        let stats = Stats {
            def_count: 2,
            file_count: 1,
            edges_by_kind: EdgesByKind::default(),
            ambiguous_count: 0,
            ambiguous_pct: Percent1::zero(),
            unresolved_external_count: 0,
            heuristic_edge_count: 0,
            test_def_count: 0,
            heuristic_by_tier: HeuristicByTier::default(),
            ts: None,
        };
        let json = serde_json::to_string(&stats).unwrap();
        assert!(
            json.ends_with(
                r#""heuristic_edge_count":0,"test_def_count":0,"heuristic_by_tier":{"ext":0,"guess":0}}"#
            ),
            "heuristic_by_tier is LAST, after test_def_count, and both its keys are always written: {json}"
        );
    }

    /// The same append-last rule for a TS repo, which is the only tree where
    /// the two optional tail keys can both appear: `ts` was added first and
    /// `heuristic_by_tier` after it, so `heuristic_by_tier` still ends the
    /// block and `ts` sits between it and `test_def_count`. A reader diffing a
    /// TS graph against an older one sees each new fact appended, never
    /// inserted ahead of an older key.
    #[test]
    fn stats_keeps_heuristic_by_tier_last_even_when_a_ts_block_is_present() {
        let stats = Stats {
            def_count: 0,
            file_count: 0,
            edges_by_kind: EdgesByKind::default(),
            ambiguous_count: 0,
            ambiguous_pct: Percent1::zero(),
            unresolved_external_count: 0,
            heuristic_edge_count: 0,
            test_def_count: 0,
            heuristic_by_tier: HeuristicByTier::default(),
            ts: Some(crate::tsgraph::TsStats {
                ts_file_count: 1,
                ts_def_count: 2,
                external_import_count: 3,
                unresolved_ref_count: 4,
            }),
        };
        let json = serde_json::to_string(&stats).unwrap();
        assert!(
            json.ends_with(concat!(
                r#""test_def_count":0,"#,
                r#""ts":{"ts_file_count":1,"ts_def_count":2,"external_import_count":3,"unresolved_ref_count":4},"#,
                r#""heuristic_by_tier":{"ext":0,"guess":0}}"#
            )),
            "key order must be test_def_count, ts, heuristic_by_tier: {json}"
        );
    }

    // --- Edge: shape-per-kind, tag first ---------------------------------

    #[test]
    fn imports_edge_has_target_not_to() {
        let e = Edge::Imports {
            from_file: "F.cs".into(),
            from_line: 1,
            target: "System".into(),
        };
        let json = serde_json::to_string(&e).unwrap();
        assert_eq!(
            json,
            r#"{"kind":"imports","from_file":"F.cs","from_line":1,"target":"System"}"#
        );
    }

    #[test]
    fn uses_type_edge_shape() {
        let e = Edge::UsesType {
            from_file: "F.cs".into(),
            from_line: 1,
            to: "Ns.T".into(),
            to_file: "Ns/T.cs".into(),
            heuristic: false,
        };
        let json = serde_json::to_string(&e).unwrap();
        assert_eq!(
            json,
            r#"{"kind":"uses-type","from_file":"F.cs","from_line":1,"to":"Ns.T","to_file":"Ns/T.cs"}"#
        );
    }

    // The serialized shape in one assertion: `heuristic` is the LAST key, it
    // appears only when set, and a precise edge of the same kind is
    // byte-for-byte what it was before the tag existed.
    #[test]
    fn heuristic_flag_is_appended_last_and_omitted_when_false() {
        let precise = Edge::UsesMember {
            from_file: "F.cs".into(),
            from_line: 1,
            to: "Ns.T".into(),
            to_file: "Ns/T.cs".into(),
            heuristic: false,
            tier: None,
            member: None,
        };
        assert_eq!(
            serde_json::to_string(&precise).unwrap(),
            r#"{"kind":"uses-member","from_file":"F.cs","from_line":1,"to":"Ns.T","to_file":"Ns/T.cs"}"#
        );
        let guess = Edge::UsesMember {
            from_file: "F.cs".into(),
            from_line: 1,
            to: "Ns.T".into(),
            to_file: "Ns/T.cs".into(),
            heuristic: true,
            tier: Some(HeuristicTier::Guess),
            member: Some("M".into()),
        };
        assert_eq!(
            serde_json::to_string(&guess).unwrap(),
            r#"{"kind":"uses-member","from_file":"F.cs","from_line":1,"to":"Ns.T","to_file":"Ns/T.cs","heuristic":true,"tier":"guess","member":"M"}"#
        );
        let ext = Edge::UsesMember {
            from_file: "F.cs".into(),
            from_line: 1,
            to: "Ns.T".into(),
            to_file: "Ns/T.cs".into(),
            heuristic: true,
            tier: Some(HeuristicTier::Ext),
            member: Some("M".into()),
        };
        assert_eq!(
            serde_json::to_string(&ext).unwrap(),
            r#"{"kind":"uses-member","from_file":"F.cs","from_line":1,"to":"Ns.T","to_file":"Ns/T.cs","heuristic":true,"tier":"ext","member":"M"}"#
        );
        // And it reads back: an edge written by either runtime round-trips
        // with the flag intact, absent meaning precise -- and now with its
        // tier and member intact too, which is what makes an older graph.json
        // (neither key written) still parse, as two `None`s.
        assert_eq!(
            serde_json::from_str::<Edge>(&serde_json::to_string(&guess).unwrap()).unwrap(),
            guess
        );
        assert_eq!(
            serde_json::from_str::<Edge>(&serde_json::to_string(&ext).unwrap()).unwrap(),
            ext
        );
        assert_eq!(
            serde_json::from_str::<Edge>(&serde_json::to_string(&precise).unwrap()).unwrap(),
            precise
        );
    }

    // The append ORDER, pinned on its own: `heuristic`, then `tier`, then
    // `member`, each omitted when it has nothing to say. A precise edge that
    // does name its member -- which is every precise uses-member edge the
    // resolver emits -- carries `member` and nothing else, so its bytes gain
    // exactly one key over the pre-tier shape.
    #[test]
    fn uses_member_edge_appends_tier_then_member_after_heuristic_and_omits_both_when_precise() {
        let precise = Edge::uses_member(
            "F.cs".into(),
            1,
            "Ns.T".into(),
            "Ns/T.cs".into(),
            Some("M".into()),
            None,
        );
        assert_eq!(
            serde_json::to_string(&precise).unwrap(),
            r#"{"kind":"uses-member","from_file":"F.cs","from_line":1,"to":"Ns.T","to_file":"Ns/T.cs","member":"M"}"#
        );
        assert!(!precise.is_heuristic(), "no tier means no guess");
        assert_eq!(precise.tier(), None);

        for (tier, word) in [(HeuristicTier::Ext, "ext"), (HeuristicTier::Guess, "guess")] {
            let e = Edge::uses_member(
                "F.cs".into(),
                1,
                "Ns.T".into(),
                "Ns/T.cs".into(),
                Some("M".into()),
                Some(tier),
            );
            assert_eq!(
                serde_json::to_string(&e).unwrap(),
                format!(
                    r#"{{"kind":"uses-member","from_file":"F.cs","from_line":1,"to":"Ns.T","to_file":"Ns/T.cs","heuristic":true,"tier":"{word}","member":"M"}}"#
                ),
                "heuristic, then tier, then member"
            );
            // The constructor is what makes the flag and the tier one fact:
            // pass a tier and the edge is a guess, pass none and it is not.
            assert!(e.is_heuristic());
            assert_eq!(e.tier(), Some(tier));
        }

        // The two kinds that carry the flag but no tier answer `None` rather
        // than guessing on the reader's behalf.
        assert_eq!(
            Edge::UsesType {
                from_file: "F.cs".into(),
                from_line: 1,
                to: "Ns.T".into(),
                to_file: "Ns/T.cs".into(),
                heuristic: true,
            }
            .tier(),
            None
        );
    }

    #[test]
    fn ambiguous_edge_shape() {
        let e = Edge::Ambiguous {
            origin: "uses-type".into(),
            from_file: "F.cs".into(),
            from_line: 4,
            raw: "Money".into(),
            candidates: vec![Candidate {
                id: "A.Money".into(),
                file: "A/Money.cs".into(),
            }],
            candidate_count: 2,
        };
        let json = serde_json::to_string(&e).unwrap();
        assert_eq!(
            json,
            r#"{"kind":"ambiguous","origin":"uses-type","from_file":"F.cs","from_line":4,"raw":"Money","candidates":[{"id":"A.Money","file":"A/Money.cs"}],"candidate_count":2}"#
        );
    }

    // --- graph.json: `units` is appended after `names` --------------------

    fn empty_stats() -> Stats {
        Stats {
            def_count: 0,
            file_count: 0,
            edges_by_kind: EdgesByKind::default(),
            ambiguous_count: 0,
            ambiguous_pct: Percent1::zero(),
            unresolved_external_count: 0,
            heuristic_edge_count: 0,
            test_def_count: 0,
            heuristic_by_tier: HeuristicByTier::default(),
            ts: None,
        }
    }

    // The two halves of the `units` contract in one place: a graph whose
    // repo declares no project must serialize with NO `units` key at all
    // (that is what keeps every csproj-less tree byte-identical to what it
    // was), and one that does must carry `units` LAST -- after `names` --
    // with each row keyed `id`, `name`, `refs`, `test` in that order and the
    // last two omitted at their empty/false value. Byte literals on purpose:
    // a golden recomputed by the code under test proves nothing.
    #[test]
    fn graph_omits_units_when_empty_and_appends_them_after_names_otherwise() {
        let mut g = Graph {
            schema_version: GRAPH_SCHEMA_VERSION,
            built_at_head: None,
            defs: Vec::new(),
            edges: Vec::new(),
            stats: empty_stats(),
            names: vec![GraphName {
                name: "A".to_string(),
                kind: "class".to_string(),
                file: "A/A.cs".to_string(),
                line: 1,
                owner: String::new(),
            }],
            units: Vec::new(),
        };

        const WITHOUT_UNITS: &str = concat!(
            r#"{"schema_version":2,"built_at_head":null,"defs":[],"edges":[],"stats":{"def_count":0,"#,
            r#""file_count":0,"edges_by_kind":{"inherits":0,"uses-type":0,"imports":0,"uses-member":0,"#,
            r#""ctor-di":0},"ambiguous_count":0,"ambiguous_pct":0,"unresolved_external_count":0,"#,
            r#""heuristic_edge_count":0,"test_def_count":0,"heuristic_by_tier":{"ext":0,"guess":0}},"#,
            r#""names":[{"name":"A","kind":"class","file":"A/A.cs","line":1}]}"#,
        );
        assert_eq!(
            serde_json::to_string(&g).unwrap(),
            WITHOUT_UNITS,
            "an empty unit list must not emit a `units` key at all"
        );

        g.units = vec![
            GraphUnit {
                id: "A/A.csproj".to_string(),
                name: "A".to_string(),
                refs: vec!["B/B.csproj".to_string()],
                test: false,
            },
            GraphUnit {
                id: "B/B.csproj".to_string(),
                name: "B".to_string(),
                refs: Vec::new(),
                test: false,
            },
            GraphUnit {
                id: "T/T.Tests.csproj".to_string(),
                name: "T.Tests".to_string(),
                refs: vec!["A/A.csproj".to_string()],
                test: true,
            },
        ];

        const WITH_UNITS: &str = concat!(
            r#""names":[{"name":"A","kind":"class","file":"A/A.cs","line":1}],"#,
            r#""units":[{"id":"A/A.csproj","name":"A","refs":["B/B.csproj"]},"#,
            r#"{"id":"B/B.csproj","name":"B"},"#,
            r#"{"id":"T/T.Tests.csproj","name":"T.Tests","refs":["A/A.csproj"],"test":true}]}"#,
        );
        let json = serde_json::to_string(&g).unwrap();
        assert_eq!(
            json,
            format!(
                "{}{}",
                WITHOUT_UNITS
                    .strip_suffix(
                        r#""names":[{"name":"A","kind":"class","file":"A/A.cs","line":1}]}"#
                    )
                    .unwrap(),
                WITH_UNITS
            ),
            "`units` is appended after `names` and changes nothing before it"
        );

        // And a graph.json written before `units` existed still reads back --
        // the field defaults rather than failing the parse.
        let reparsed: Graph = serde_json::from_str(WITHOUT_UNITS).unwrap();
        assert!(reparsed.units.is_empty());
        let round_tripped: Graph = serde_json::from_str(&json).unwrap();
        assert_eq!(round_tripped.units, g.units);
    }

    // --- Stats: fixed edges_by_kind order ---------------------------------

    #[test]
    fn edges_by_kind_field_order_is_fixed_not_alphabetical() {
        let s = EdgesByKind {
            inherits: 1,
            uses_type: 2,
            imports: 3,
            uses_member: 4,
            ctor_di: 5,
            ..Default::default()
        };
        let json = serde_json::to_string(&s).unwrap();
        assert_eq!(
            json,
            r#"{"inherits":1,"uses-type":2,"imports":3,"uses-member":4,"ctor-di":5}"#
        );
    }

    // --- The cache holds two fragment shapes -------------------

    // The untagged discrimination is what keeps one cache file able to hold
    // both shapes: read the wrong arm and a whole repo's fragments come back
    // silently empty. Both directions are pinned here, on the exact
    // serialized bytes.
    #[test]
    fn any_fragment_round_trips_both_shapes_and_never_reads_one_as_the_other() {
        let cs = AnyFragment::Cs(Fragment {
            defs: Vec::new(),
            usings: Vec::new(),
            refs: Vec::new(),
            names: Vec::new(),
        });
        let cs_json = serde_json::to_string(&cs).unwrap();
        assert_eq!(cs_json, r#"{"defs":[],"usings":[],"refs":[],"names":[]}"#);
        assert!(matches!(
            serde_json::from_str::<AnyFragment>(&cs_json).unwrap(),
            AnyFragment::Cs(_)
        ));

        let ts = AnyFragment::Ts(extract::TsFragment {
            ts: 1,
            defs: vec![extract::TsFragmentDef {
                name: "x".into(),
                kind: "const".into(),
                line: 1,
                end_line: 1,
            }],
            imports: Vec::new(),
            reexports: Vec::new(),
            refs: Vec::new(),
            default: None,
        });
        let ts_json = serde_json::to_string(&ts).unwrap();
        assert_eq!(
            ts_json,
            r#"{"ts":1,"defs":[{"name":"x","kind":"const","line":1,"endLine":1}],"imports":[],"reexports":[],"refs":[]}"#
        );
        assert!(matches!(
            serde_json::from_str::<AnyFragment>(&ts_json).unwrap(),
            AnyFragment::Ts(_)
        ));
        assert_eq!(
            serde_json::from_str::<AnyFragment>(&ts_json).unwrap(),
            ts,
            "and round-trips to the same value"
        );
    }

    // The four TS counts land AFTER `ctor-di`, in this order, and
    // only when the repo carries a TS fragment at all: a C#-only repo's stats
    // block keeps the exact bytes the assertion above pins.
    #[test]
    fn edges_by_kind_appends_the_four_ts_counts_after_ctor_di_when_present() {
        let s = EdgesByKind {
            inherits: 1,
            uses_type: 2,
            imports: 3,
            uses_member: 4,
            ctor_di: 5,
            import: Some(6),
            call: Some(7),
            jsx_use: Some(8),
            dispatch: Some(9),
        };
        let json = serde_json::to_string(&s).unwrap();
        assert_eq!(
            json,
            r#"{"inherits":1,"uses-type":2,"imports":3,"uses-member":4,"ctor-di":5,"import":6,"call":7,"jsx-use":8,"dispatch":9}"#
        );
    }

    // --- atomic writes: crash-sim -----------------------------------

    #[test]
    fn atomic_write_leaves_target_intact_when_only_a_stray_tmp_exists() {
        let dir = temp_dir("atomic-crash");
        let target = dir.join("graph.json");
        fs::write(&target, b"{\"old\":true}").unwrap();
        // Simulate a crashed prior write: a tmp file was created but the
        // process died before the rename -- the target must be completely
        // unaffected by the stray file's mere presence.
        fs::write(dir.join(".graph.json.tmp.99999.7"), b"GARBAGE-PARTIAL").unwrap();
        assert_eq!(fs::read_to_string(&target).unwrap(), "{\"old\":true}");
    }

    #[test]
    fn atomic_write_replaces_target_and_leaves_no_tmp_file_behind() {
        let dir = temp_dir("atomic-clean");
        let target = dir.join("graph.json");
        fs::write(&target, b"{\"old\":true}").unwrap();
        atomic_write_bytes(&target, b"{\"new\":true}").unwrap();
        assert_eq!(fs::read_to_string(&target).unwrap(), "{\"new\":true}");
        let leftover: Vec<_> = fs::read_dir(&dir)
            .unwrap()
            .filter_map(|e| e.ok())
            .filter(|e| e.file_name().to_string_lossy().contains(".tmp."))
            .collect();
        assert!(
            leftover.is_empty(),
            "no tmp file should remain: {leftover:?}"
        );
    }

    #[test]
    fn atomic_write_creates_parent_directories() {
        let dir = temp_dir("atomic-mkdir");
        let target = dir.join("nested").join("deeper").join("graph.json");
        atomic_write_bytes(&target, b"{}").unwrap();
        assert_eq!(fs::read_to_string(&target).unwrap(), "{}");
    }

    // --- rebuild_graph: unchanged path never touches the graph -----------

    #[test]
    fn rebuild_graph_skips_when_unchanged_and_graph_already_exists() {
        let dir = temp_dir("rebuild-unchanged");
        fs::create_dir_all(graph_dir(&dir)).unwrap();
        fs::write(graph_json_path(&dir), b"{\"schema_version\":2,\"built_at_head\":null,\"defs\":[],\"edges\":[],\"stats\":{\"def_count\":0,\"file_count\":0,\"edges_by_kind\":{\"inherits\":0,\"uses-type\":0,\"imports\":0,\"uses-member\":0},\"ambiguous_count\":0,\"ambiguous_pct\":0,\"unresolved_external_count\":0}}").unwrap();
        let outcome = rebuild_graph(&dir, &[], &HashMap::new(), false, None).unwrap();
        assert!(matches!(outcome, RebuildOutcome::NotRebuilt));
    }

    // The other half of that fast path: "nothing changed" is not enough on
    // its own. A graph.json written by a build that predates the current
    // schema is missing facts every reader now expects, so it is rebuilt
    // even though not one fragment moved -- the ONLY thing separating this
    // case from the one above is the version in its first bytes.
    #[test]
    fn rebuild_graph_rebuilds_when_the_existing_graph_carries_an_older_schema_version() {
        let dir = temp_dir("rebuild-old-schema");
        fs::create_dir_all(graph_dir(&dir)).unwrap();
        fs::write(graph_json_path(&dir), b"{\"schema_version\":1,\"built_at_head\":null,\"defs\":[],\"edges\":[],\"stats\":{\"def_count\":0,\"file_count\":0,\"edges_by_kind\":{\"inherits\":0,\"uses-type\":0,\"imports\":0,\"uses-member\":0},\"ambiguous_count\":0,\"ambiguous_pct\":0,\"unresolved_external_count\":0}}").unwrap();
        let outcome = rebuild_graph(&dir, &[], &HashMap::new(), false, None).unwrap();
        let RebuildOutcome::Rebuilt(graph) = outcome else {
            panic!("an older-schema graph must be rebuilt on the unchanged path");
        };
        assert_eq!(graph.schema_version, GRAPH_SCHEMA_VERSION);
        assert!(
            fs::read_to_string(graph_json_path(&dir))
                .unwrap()
                .starts_with(r#"{"schema_version":2,"#),
            "and the rebuilt artifact carries the current version on disk"
        );
    }

    // A truncated or unreadable artifact answers the same way an older one
    // does -- rebuild -- rather than being trusted or panicking.
    #[test]
    fn rebuild_graph_rebuilds_when_the_existing_graph_is_too_short_to_carry_a_version() {
        let dir = temp_dir("rebuild-truncated");
        fs::create_dir_all(graph_dir(&dir)).unwrap();
        fs::write(graph_json_path(&dir), b"{").unwrap();
        assert!(!graph_schema_is_current(&dir));
        assert!(matches!(
            rebuild_graph(&dir, &[], &HashMap::new(), false, None).unwrap(),
            RebuildOutcome::Rebuilt(_)
        ));
    }

    #[test]
    fn rebuild_graph_reuses_a_cached_fragment_at_matching_mtime() {
        let dir = temp_dir("rebuild-cache-hit");
        let fragment = Fragment {
            defs: vec![FragDef {
                id: "A".into(),
                name: "A".into(),
                namespace: "".into(),
                kind: "class".into(),
                line: 1,
                methods: vec![],
                properties: vec![],
                fields: vec![],
                method_returns: OrderedMap::new(),
                extension_methods: vec![],
                bases: vec![],
                type_params: vec![],
                base_generic_args: OrderedMap::new(),
                test_methods: vec![],
                property_types: OrderedMap::new(),
                field_types: OrderedMap::new(),
                method_return_args: OrderedMap::new(),
                non_public_methods: vec![],
                method_arities: OrderedMap::new(),
                method_params: OrderedMap::new(),
                end_line: 1,
            }],
            usings: vec![],
            refs: vec![],
            names: vec![],
        };
        // First build: nothing cached, comes from fresh_fragments.
        let mut fresh = HashMap::new();
        fresh.insert("A.cs".to_string(), AnyFragment::Cs(fragment.clone()));
        let graph_files = vec![GraphFile {
            rel: "A.cs".to_string(),
            mtime: 111,
        }];
        let first = rebuild_graph(&dir, &graph_files, &fresh, true, None).unwrap();
        assert!(matches!(first, RebuildOutcome::Rebuilt(_)));

        // Second build: same mtime, EMPTY fresh_fragments -- must reuse the
        // cache, not silently drop the file from the graph.
        let empty: HashMap<String, AnyFragment> = HashMap::new();
        let second = rebuild_graph(&dir, &graph_files, &empty, true, None).unwrap();
        match second {
            RebuildOutcome::Rebuilt(g) => {
                assert_eq!(g.defs.len(), 1, "cached fragment must still be used")
            }
            RebuildOutcome::NotRebuilt => panic!("changed=true must always rebuild"),
        }
    }

    // --- The v13 cache generation --------------------------

    #[test]
    fn rebuild_graph_writes_the_v13_caches_and_deletes_every_superseded_generation() {
        let dir = temp_dir("rebuild-v13");
        fs::create_dir_all(graph_dir(&dir)).unwrap();
        // The v9 pair joined this list when fragments gained def
        // `typeParams`/`baseGenericArgs` and the `ctor-param` ref kind, so a v9
        // fragment read back today carries none and every ctor-DI fact would be
        // missing from the graph. The v10 pair joined when a markup
        // fragment gained the `x:Class` def and its element/binding refs, so a
        // v10 markup fragment read back carries names only and every XAML
        // declaration and instantiation would be missing from the graph. The v11
        // pair joined when a `.ts/.tsx/.js/.jsx` file gained a reference
        // fragment where it previously had none at all, so a v11 cache read back
        // would leave every TS/JS rel looking like a file the worker never saw.
        // This side records no TS fragment yet, but the cache generation is
        // shared -- two writers putting two generations into one git dir would
        // have each delete the other's cache on every map. The v12 pair joined
        // when defs gained propertyTypes and refs
        // gained receiverPropertyOwner and the receiverCallOwner/
        // receiverCallMember pair, so a v12 fragment read back carries none and
        // every property hop and every var-from-invocation receiver would
        // silently stay unresolved.
        assert_eq!(SUPERSEDED_CACHE_FILES.len(), 34, "v1..v17 pairs");
        for stale in SUPERSEDED_CACHE_FILES {
            fs::write(graph_dir(&dir).join(stale), b"{}").unwrap();
        }

        let fragment = Fragment {
            defs: vec![FragDef {
                id: "App.A".into(),
                name: "A".into(),
                namespace: "App".into(),
                kind: "class".into(),
                line: 1,
                methods: vec![],
                properties: vec![],
                fields: vec![],
                method_returns: OrderedMap::new(),
                extension_methods: vec![],
                bases: vec![],
                type_params: vec![],
                base_generic_args: OrderedMap::new(),
                test_methods: vec![],
                property_types: OrderedMap::new(),
                field_types: OrderedMap::new(),
                method_return_args: OrderedMap::new(),
                non_public_methods: vec![],
                method_arities: OrderedMap::new(),
                method_params: OrderedMap::new(),
                end_line: 1,
            }],
            usings: vec![],
            refs: vec![],
            names: vec![],
        };
        let mut fresh = HashMap::new();
        fresh.insert("src/A.cs".to_string(), AnyFragment::Cs(fragment));
        let graph_files = vec![GraphFile {
            rel: "src/A.cs".to_string(),
            mtime: 222,
        }];
        rebuild_graph(&dir, &graph_files, &fresh, true, None).unwrap();

        assert!(
            graph_dir(&dir).join("fragments-v18.json").exists(),
            "the v18 payload cache is what gets written"
        );
        assert!(
            graph_dir(&dir).join("fragments-index-v18.json").exists(),
            "and its mtime-only index alongside it"
        );
        for stale in SUPERSEDED_CACHE_FILES {
            assert!(
                !graph_dir(&dir).join(stale).exists(),
                "{stale} must be deleted -- rename IS the invalidation"
            );
        }
    }

    // --- The v18 cache generation --------------------------

    #[test]
    fn fragments_cache_v18_supersedes_v17() {
        let dir = temp_dir("fragments-cache-v18-paths");
        assert_eq!(
            fragments_cache_path(&dir),
            graph_dir(&dir).join("fragments-v18.json")
        );
        assert_eq!(
            fragments_index_path(&dir),
            graph_dir(&dir).join("fragments-index-v18.json")
        );
        assert!(
            SUPERSEDED_CACHE_FILES.contains(&"fragments-v17.json"),
            "v17 joined the superseded list when the v18 bump landed"
        );
        assert!(
            SUPERSEDED_CACHE_FILES.contains(&"fragments-index-v17.json"),
            "its index pairs with it, same as every other generation"
        );

        let dir = temp_dir("rebuild-v18");
        fs::create_dir_all(graph_dir(&dir)).unwrap();
        fs::write(graph_dir(&dir).join("fragments-v17.json"), b"{}").unwrap();
        fs::write(graph_dir(&dir).join("fragments-index-v17.json"), b"{}").unwrap();

        let fragment = Fragment {
            defs: vec![],
            usings: vec![],
            refs: vec![],
            names: vec![],
        };
        let mut fresh = HashMap::new();
        fresh.insert("src/A.cs".to_string(), AnyFragment::Cs(fragment));
        let graph_files = vec![GraphFile {
            rel: "src/A.cs".to_string(),
            mtime: 1,
        }];
        rebuild_graph(&dir, &graph_files, &fresh, true, None).unwrap();

        assert!(graph_dir(&dir).join("fragments-v18.json").exists());
        assert!(graph_dir(&dir).join("fragments-index-v18.json").exists());
        assert!(
            !graph_dir(&dir).join("fragments-v17.json").exists(),
            "the v17 pair is deleted -- rename IS the invalidation"
        );
        assert!(!graph_dir(&dir).join("fragments-index-v16.json").exists());
    }

    // --- v8: FragRef's outerTypes, appended last -----------------------------

    #[test]
    fn frag_ref_outer_types_is_appended_last_after_receiver_args() {
        let r = FragRef {
            receiver_args: Some(vec!["FutureState".into()]),
            outer_types: vec!["Outer".into(), "Inner".into()],
            ..frag_ref(false, Some("Binder"), Some(1))
        };
        let json = serde_json::to_string(&r).unwrap();
        assert_eq!(
            json,
            r#"{"kind":"uses-member","name":"repo","member":"Save","line":7,"namespace":"App.Shape","receiverType":"Binder","argCount":1,"receiverArgs":["FutureState"],"outerTypes":["Outer","Inner"]}"#
        );
        let reparsed: FragRef = serde_json::from_str(&json).unwrap();
        assert_eq!(
            reparsed.outer_types,
            vec!["Outer".to_string(), "Inner".to_string()]
        );
    }

    // --- The two chain facts, appended after outerTypes ----

    #[test]
    fn frag_ref_property_owner_and_call_pair_are_appended_last_and_omitted_when_absent() {
        let hop = FragRef {
            qualified: Some("head.Dial".into()),
            name: "Dial".into(),
            receiver_property_owner: Some("Widget".into()),
            ..frag_ref(false, None, Some(0))
        };
        assert_eq!(
            serde_json::to_string(&hop).unwrap(),
            r#"{"kind":"uses-member","name":"Dial","qualified":"head.Dial","member":"Save","line":7,"namespace":"App.Shape","argCount":0,"receiverPropertyOwner":"Widget"}"#
        );

        let from_call = FragRef {
            receiver_call_owner: Some("Factory".into()),
            receiver_call_member: Some("Make".into()),
            ..frag_ref(false, None, Some(0))
        };
        assert_eq!(
            serde_json::to_string(&from_call).unwrap(),
            r#"{"kind":"uses-member","name":"repo","member":"Save","line":7,"namespace":"App.Shape","argCount":0,"receiverCallOwner":"Factory","receiverCallMember":"Make"}"#
        );

        // An older cached fragment carries neither key, and absent must
        // read back as "no chain fact" -- which is what leaves such a ref
        // exactly where it was before this generation.
        let plain = serde_json::to_string(&frag_ref(false, Some("Binder"), Some(1))).unwrap();
        assert!(
            !plain.contains("receiverPropertyOwner") && !plain.contains("receiverCall"),
            "{plain}"
        );
        let reparsed: FragRef = serde_json::from_str(&plain).unwrap();
        assert_eq!(reparsed.receiver_property_owner, None);
        assert_eq!(reparsed.receiver_call_owner, None);
        assert_eq!(reparsed.receiver_call_member, None);
    }

    #[test]
    fn frag_ref_an_empty_or_absent_outer_types_serializes_to_nothing_and_reads_back_empty() {
        let json = serde_json::to_string(&frag_ref(false, None, None)).unwrap();
        assert!(
            !json.contains("outerTypes"),
            "a namespace-level ref keeps its exact pre-v8 bytes: {json}"
        );
        // A pre-v8 cached fragment has no key at all, and absent must mean the
        // same thing as empty -- which is what keeps it off the nested step.
        let pre_v8: FragRef = serde_json::from_str(
            r#"{"kind":"uses-type","name":"Widget","line":3,"namespace":"App.Core"}"#,
        )
        .unwrap();
        assert!(pre_v8.outer_types.is_empty());
    }

    // --- v18: FragDef's methodParams and FragRef's receiverLambda -----------

    #[test]
    fn fragment_round_trip_keeps_method_params_and_receiver_lambda() {
        let mut method_params = OrderedMap::new();
        method_params.insert(
            "Register".to_string(),
            vec![
                vec!["Action<Options>".to_string()],
                vec!["string".to_string(), "Func<Options,bool>".to_string()],
            ],
        );
        let d = FragDef {
            method_params: method_params.clone(),
            ..frag_def(&[], &[], &[], &[], &[])
        };
        let d_json = serde_json::to_string(&d).unwrap();
        assert!(
            d_json.ends_with(
                r#""methodParams":{"Register":[["Action<Options>"],["string","Func<Options,bool>"]]}}"#
            ),
            "methodParams is appended last, after methodArities: {d_json}"
        );
        let d_reparsed: FragDef = serde_json::from_str(&d_json).unwrap();
        assert_eq!(d_reparsed.method_params, method_params);

        // Absent when empty, and an absent key deserializes back to empty --
        // the safe default for every fragment cached before this field
        // existed.
        let d_plain_json = serde_json::to_string(&frag_def(&[], &[], &[], &[], &[])).unwrap();
        assert!(!d_plain_json.contains("methodParams"), "{d_plain_json}");
        let d_plain_reparsed: FragDef = serde_json::from_str(&d_plain_json).unwrap();
        assert!(d_plain_reparsed.method_params.is_empty());

        let slot = FragLambdaSlot {
            owner: "Registrar".to_string(),
            member: "Register".to_string(),
            arg_count: 1,
            arg_index: 0,
            arity: 1,
            index: 0,
        };
        let r = FragRef {
            receiver_lambda: Some(slot.clone()),
            ..frag_ref(false, None, None)
        };
        let r_json = serde_json::to_string(&r).unwrap();
        assert!(
            r_json.ends_with(
                r#""receiverLambda":{"owner":"Registrar","member":"Register","argCount":1,"argIndex":0,"arity":1,"index":0}}"#
            ),
            "receiverLambda is appended last, after receiverLocal: {r_json}"
        );
        let r_reparsed: FragRef = serde_json::from_str(&r_json).unwrap();
        assert_eq!(r_reparsed.receiver_lambda, Some(slot));

        // Absent when `None`, and an absent key deserializes back to `None`.
        let r_plain_json = serde_json::to_string(&frag_ref(false, None, None)).unwrap();
        assert!(!r_plain_json.contains("receiverLambda"), "{r_plain_json}");
        let r_plain_reparsed: FragRef = serde_json::from_str(&r_plain_json).unwrap();
        assert_eq!(r_plain_reparsed.receiver_lambda, None);
    }
}